Balanced brackets
Task:
- Generate a string with N opening brackets [ and with N closing brackets ], in some arbitrary order.
- Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.
You are encouraged to solve this task according to the task description, using any language you may know.
- Examples
(empty) OK [] OK [][] OK [[][]] OK ][ NOT OK ][][ NOT OK []][[] NOT OK
11l
F gen(n)
V txt = [‘[’, ‘]’] * n
random:shuffle(&txt)
R txt.join(‘’)
F is_balanced(s)
V nesting_level = 0
L(c) s
S c
‘[’
nesting_level++
‘]’
I --nesting_level < 0
R 0B
R 1B
L(n) 0..9
V s = gen(n)
print(s‘’(‘ ’ * (20 - s.len))‘is ’(I is_balanced(s) {‘balanced’} E ‘not balanced’))- Output:
is balanced [] is balanced []][ is not balanced ][[[]] is not balanced []][][[] is not balanced ][[][[[]]] is not balanced [[]]][[][]][ is not balanced [[]][[]]]][[][ is not balanced []]][[[[]]]]][[[ is not balanced ]][]]][[[[[]][]][[ is not balanced
360 Assembly
* Balanced brackets 28/04/2016
BALANCE CSECT
USING BALANCE,R13 base register and savearea pointer
SAVEAREA B STM-SAVEAREA(R15)
DC 17F'0'
STM STM R14,R12,12(R13)
ST R13,4(R15)
ST R15,8(R13)
LR R13,R15 establish addressability
LA R8,1 i=1
LOOPI C R8,=F'20' do i=1 to 20
BH ELOOPI
MVC C(20),=CL20' ' c=' '
LA R1,1
LA R2,10
BAL R14,RANDOMX
LR R11,R0 l=randomx(1,10)
SLA R11,1 l=l*2
LA R10,1 j=1
LOOPJ CR R10,R11 do j=1 to 2*l
BH ELOOPJ
LA R1,0
LA R2,1
BAL R14,RANDOMX
LR R12,R0 m=randomx(0,1)
LTR R12,R12 if m=0
BNZ ELSEM
MVI Q,C'[' q='['
B EIFM
ELSEM MVI Q,C']' q=']'
EIFM LA R14,C-1(R10) @c(j)
MVC 0(1,R14),Q c(j)=q
LA R10,1(R10) j=j+1
B LOOPJ
ELOOPJ BAL R14,CHECKBAL
LR R2,R0
C R2,=F'1' if checkbal=1
BNE ELSEC
MVC PG+24(2),=C'ok' rep='ok'
B EIFC
ELSEC MVC PG+24(2),=C'? ' rep='? '
EIFC XDECO R8,XDEC i
MVC PG+0(2),XDEC+10
MVC PG+3(20),C
XPRNT PG,26
LA R8,1(R8) i=i+1
B LOOPI
ELOOPI L R13,4(0,R13)
LM R14,R12,12(R13)
XR R15,R15 set return code to 0
BR R14 -------------- end
CHECKBAL CNOP 0,4 -------------- checkbal
SR R6,R6 n=0
LA R7,1 k=1
LOOPK C R7,=F'20' do k=1 to 20
BH ELOOPK
LR R1,R7 k
LA R4,C-1(R1) @c(k)
MVC CI(1),0(R4) ci=c(k)
CLI CI,C'[' if ci='['
BNE NOT1
LA R6,1(R6) n=n+1
NOT1 CLI CI,C']' if ci=']'
BNE NOT2
BCTR R6,0 n=n-1
NOT2 LTR R6,R6 if n<0
BNM NSUP0
SR R0,R0 return(0)
B RETCHECK
NSUP0 LA R7,1(R7) k=k+1
B LOOPK
ELOOPK LTR R6,R6 if n=0
BNZ ELSEN
LA R0,1 return(1)
B RETCHECK
ELSEN SR R0,R0 return(0)
RETCHECK BR R14 -------------- end checkbal
RANDOMX CNOP 0,4 -------------- randomx
LR R3,R2 i2
SR R3,R1 ii=i2-i1
L R5,SEED
M R4,=F'1103515245'
A R5,=F'12345'
SRDL R4,1 shift to improve the algorithm
ST R5,SEED seed=(seed*1103515245+12345)>>1
LR R6,R3 ii
LA R6,1(R6) ii+1
L R5,SEED seed
LA R4,0 clear
DR R4,R6 seed//(ii+1)
AR R4,R1 +i1
LR R0,R4 return(seed//(ii+1)+i1)
BR R14 -------------- end randomx
SEED DC F'903313037'
C DS 20CL1
Q DS CL1
CI DS CL1
PG DC CL80' '
XDEC DS CL12
REGS
END BALANCE- Output:
1 ][[[][[] ? 2 ]][]][][[[[][[ ? 3 [] ok 4 ][ ? 5 ][[][]]]]] ? 6 ][]] ? 7 ]][][][]]] ? 8 [[[[][[[[][[]] ? 9 ][[]][[[[[[[[[]]][ ? 10 ]]]][][[][]]][][[[ ? 11 [][[]][][][[[] ? 12 ]] ? 13 [][[[]]] ok 14 ][ ? 15 []][ ? 16 ][[]][]]][[] ? 17 ][][]] ? 18 [] ok 19 [[[[[[][[[[[][][ ? 20 [[][[][] ?
AArch64 Assembly
/* ARM assembly AARCH64 Raspberry PI 3B */
/* program balencebrac64.s */
/************************************/
/* Constantes */
/************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"
/*********************************/
/* Initialized data */
/*********************************/
.data
szMessResult: .asciz "Expression : "
szMessBalenced: .asciz " balanced"
szMessNotBalenced: .asciz " not balanced"
szMessStart: .asciz "Program 64 bits start.\n"
szCarriageReturn: .asciz "\n"
/*********************************/
/* UnInitialized data */
/*********************************/
.bss
sZoneConv: .skip 24 // conversion buffer
sBuffer: .skip 80
/*********************************/
/* code section */
/*********************************/
.text
.global main
main: // entry of program
ldr x0,qAdrszMessStart
bl affichageMess
mov x0,0b111000 // bit 1 = open bracket bit 0 = close bracket
bl testBalanced
mov x0,0b110100
bl testBalanced
mov x0,0b11001001
bl testBalanced
mov x19,10 // number random test
1:
mov x0,1 // mini number
mov x1,10000 // maxi random number
bl extRandom // generate random number
bl testBalanced
subs x19,x19,1
bge 1b
100: // standard end of the program
mov x0, #0 // return code
mov x8,EXIT
svc #0 // perform the system call
qAdrszCarriageReturn: .quad szCarriageReturn
qAdrszMessResult: .quad szMessResult
qAdrszMessNotBalenced: .quad szMessNotBalenced
qAdrszMessBalenced: .quad szMessBalenced
qAdrszMessStart: .quad szMessStart
qAdrsBuffer: .quad sBuffer
/***************************************************/
/* routine to test expression */
/***************************************************/
/* x0 expression */
testBalanced:
stp x1,lr,[sp,-16]! // save registres
stp x2,x3,[sp,-16]! // save registres
ldr x1,qAdrsBuffer
bl isBalanced
cmp x0,0
ldr x3,qAdrszMessNotBalenced
ldr x4,qAdrszMessBalenced
csel x3,x3,x4,eq
mov x0,#4 // string number to display
ldr x1,qAdrszMessResult
ldr x2,qAdrsBuffer
ldr x4,qAdrszCarriageReturn
bl displayStrings // display message
100:
ldp x2,x3,[sp],16 // restaur registres
ldp x1,lr,[sp],16 // restaur registres
ret
/***************************************************/
/* control if expression is balenced */
/***************************************************/
/* x0 expression */
/* x1 buffer address */
/* x0 return 1 if balanced else zero */
isBalanced:
stp x1,lr,[sp,-16]! // save registres
stp x2,x3,[sp,-16]! // save registres
mov x3,63
clz x2,x0 // number of zeros on the left
sub x2,x3,x2 // so many useful numbers right
mov x4,1 // mask to test bit
lsl x4,x4,x2 // shift left begin expression
mov x3,0 // top if right bracket > left bracket
mov x7,0 // indice display buffer expression
mov x5,0 // counter brackets
1: // begin loop to test bits
tst x0,x4
beq 2f // bit = 0
mov x6,'(' // else bit = 1 -> open bracket
strb w6,[x1,x7] // store in buffer
add x7,x7,1 // increment indice
add x5,x5,1 // increment open bracket
b 3f
2: // bit = 0
mov x6,')' // close bracket
strb w6,[x1,x7] // store in buffer
add x7,x7,1 // increment indice
subs x5,x5,1 // decrement open bracket
bge 3f // if negative
mov x3,1 // top error
3:
lsr x4,x4,1 // shift mask right
cbnz x4,1b // and loop if not zero
strb wzr,[x1,x7] // zero final on buffer
cmp x5,0 // right bracket <> left bracket -> error
bne 4f
cmp x3,0 // in expression left bracket > right bracket
bne 4f
mov x0,1 // balanced
b 100f
4:
mov x0,0 // not balanced
100:
ldp x2,x3,[sp],16 // restaur registres
ldp x1,lr,[sp],16 // restaur registres
ret
/***************************************************/
/* display multi strings */
/* new version 24/05/2023 */
/***************************************************/
/* x0 contains number strings address */
/* x1 address string1 */
/* x2 address string2 */
/* x3 address string3 */
/* x4 address string4 */
/* x5 address string5 */
/* x6 address string5 */
/* x7 address string6 */
displayStrings: // INFO: displayStrings
stp x8,lr,[sp,-16]! // save registers
stp x2,fp,[sp,-16]! // save registers
add fp,sp,#32 // save paraméters address (4 registers saved * 8 bytes)
mov x8,x0 // save strings number
cmp x8,#0 // 0 string -> end
ble 100f
mov x0,x1 // string 1
bl affichageMess
cmp x8,#1 // number > 1
ble 100f
mov x0,x2
bl affichageMess
cmp x8,#2
ble 100f
mov x0,x3
bl affichageMess
cmp x8,#3
ble 100f
mov x0,x4
bl affichageMess
cmp x8,#4
ble 100f
mov x0,x5
bl affichageMess
cmp x8,#5
ble 100f
mov x0,x6
bl affichageMess
cmp x8,#6
ble 100f
mov x0,x7
bl affichageMess
100:
ldp x2,fp,[sp],16 // restaur registers
ldp x8,lr,[sp],16 // restaur registers
ret
/******************************************************************/
/* random number */
/******************************************************************/
/* x0 contains inferior value */
/* x1 contains maxi value */
/* x0 return random number */
extRandom:
stp x1,lr,[sp,-16]! // save registers
stp x2,x8,[sp,-16]! // save registers
stp x19,x20,[sp,-16]! // save registers
sub sp,sp,16 // reserve 16 octets on stack
mov x19,x0
add x20,x1,1
mov x0,sp // store result on stack
mov x1,8 // length 8 bytes
mov x2,0
mov x8,278 // call system Linux 64 bits Urandom
svc 0
mov x0,sp // load résult on stack
ldr x0,[x0]
sub x2,x20,x19 // calculation of the range of values
udiv x1,x0,x2 // calculation range modulo
msub x0,x1,x2,x0
add x0,x0,x19 // and add inferior value
100:
add sp,sp,16 // alignement stack
ldp x19,x20,[sp],16 // restaur 2 registers
ldp x2,x8,[sp],16 // restaur 2 registers
ldp x1,lr,[sp],16 // restaur 2 registers
ret // retour adresse lr x30
/***************************************************/
/* ROUTINES INCLUDE */
/***************************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeARM64.inc"- Output:
Program 64 bits start. Expression : ((())) balanced Expression : (()()) balanced Expression : (())())( not balanced Expression : ((()))))()))) not balanced Expression : (()())())())) not balanced Expression : ()(((()((()) not balanced Expression : ())()(()())() not balanced Expression : ())))((()))((( not balanced Expression : (())()())(() not balanced Expression : ())()))))(()( not balanced Expression : ())()(())(()( not balanced Expression : ())(()(()())) not balanced Expression : ((()))()))))) not balanced Expression : (()))((()))( not balanced
ABAP
CLASS lcl_balanced_brackets DEFINITION.
PUBLIC SECTION.
CLASS-METHODS:
class_constructor,
are_brackets_balanced
IMPORTING
seq TYPE string
RETURNING
VALUE(r_are_brackets_balanced) TYPE abap_bool,
get_random_brackets_seq
IMPORTING
n TYPE i
RETURNING
VALUE(r_bracket_seq) TYPE string.
PRIVATE SECTION.
CLASS-DATA: random_int TYPE REF TO cl_abap_random_int.
CLASS-METHODS:
_split_string
IMPORTING
i_text TYPE string
RETURNING
VALUE(r_chars) TYPE stringtab,
_rand_bool
RETURNING
VALUE(r_bool) TYPE i.
ENDCLASS.
CLASS lcl_balanced_brackets IMPLEMENTATION.
METHOD class_constructor.
random_int = cl_abap_random_int=>create( seed = CONV #( sy-uzeit )
min = 0
max = 1 ).
ENDMETHOD.
METHOD are_brackets_balanced.
DATA: open_bracket_count TYPE i.
DATA(chars) = _split_string( seq ).
r_are_brackets_balanced = abap_false.
LOOP AT chars ASSIGNING FIELD-SYMBOL(<c>).
IF <c> = ']' AND open_bracket_count = 0.
RETURN.
ENDIF.
IF <c> = ']'.
open_bracket_count = open_bracket_count - 1.
ENDIF.
IF <c> = '['.
open_bracket_count = open_bracket_count + 1.
ENDIF.
ENDLOOP.
IF open_bracket_count > 0.
RETURN.
ENDIF.
r_are_brackets_balanced = abap_true.
ENDMETHOD.
METHOD get_random_brackets_seq.
DATA(itab) = VALUE stringtab( FOR i = 1 THEN i + 1 WHILE i <= n
( COND #( WHEN _rand_bool( ) = 0 THEN '['
ELSE ']' ) ) ).
r_bracket_seq = concat_lines_of( itab ).
ENDMETHOD.
METHOD _rand_bool.
r_bool = random_int->get_next( ).
ENDMETHOD.
METHOD _split_string.
DATA: off TYPE i VALUE 0.
DO strlen( i_text ) TIMES.
INSERT i_text+off(1) INTO TABLE r_chars.
off = off + 1.
ENDDO.
ENDMETHOD.
ENDCLASS.
START-OF-SELECTION.
DO 10 TIMES.
DATA(seq) = lcl_balanced_brackets=>get_random_brackets_seq( 10 ).
cl_demo_output=>write( |{ seq } => { COND string( WHEN lcl_balanced_brackets=>are_brackets_balanced( seq ) = abap_true THEN 'OK'
ELSE 'NOT OK' ) }| ).
ENDDO.
cl_demo_output=>display( ).
- Output:
[[]][[]]]] => NOT OK ][]][[][][ => NOT OK [][]]][[[] => NOT OK ][][[[][[] => NOT OK [[[][]]][] => OK ][][]][[[[ => NOT OK ][][[[[]][ => NOT OK ][[][]][[] => NOT OK [[]][[]][] => OK [][]]][]]] => NOT OK
Action!
PROC Generate(BYTE size CHAR ARRAY s)
BYTE i,half
s(0)=size
half=size RSH 1
FOR i=1 TO half
DO s(i)='[ OD
FOR i=half+1 TO size
DO s(i)='] OD
RETURN
PROC Shuffle(CHAR ARRAY s)
BYTE i,j,k,n,len,tmp
len=s(0)
n=Rand(len+1)
FOR k=1 TO n
DO
i=Rand(len)+1
j=Rand(len)+1
tmp=s(i)
s(i)=s(j)
s(j)=tmp
OD
RETURN
BYTE FUNC Balanced(CHAR ARRAY s)
INT i,lev
lev=0
FOR i=1 TO s(0)
DO
IF s(i)='[ THEN
lev==+1
ELSE
lev==-1
FI
IF lev<0 THEN
RETURN (0)
FI
OD
IF lev#0 THEN
RETURN (0)
FI
RETURN (1)
PROC Main()
CHAR ARRAY s(20)
BYTE i,b
FOR i=0 TO 20 STEP 2
DO
Generate(i,s)
Shuffle(s)
b=Balanced(s)
IF s(0)=0 THEN
Print("(empty)")
ELSE
Print(s)
FI
Print(" is ")
IF b=0 THEN
Print("not ")
FI
PrintE("balanced")
OD
RETURN- Output:
Screenshot from Atari 8-bit computer
(empty) is balanced [] is balanced [[]] is balanced ][][[] is not balanced []][[][] is not balanced [[[]]]][[] is not balanced [[[[[[]]]]]] is balanced [[]][[[][]]][] is balanced [[[[]][[]]]][]][ is not balanced ][][][[[[[]]][]]][ is not balanced [[[[][][][][]][]]][] is balanced
Acurity Architect
Using #HASH-OFF
FUNCTION bBRACKETS_MATCH(zStringWithBrackets: STRING): STRING
VAR sCount: SHORT
VAR sBracketCounter: SHORT
VAR zOK: STRING
//
SET zOK = "NOT OK"
DO sCount = 1 TO LENGTH(zStringWithBrackets)
CASE SUBSTR(zStringWithBrackets, sCount, 1)
VALUE "["
SET sBracketCounter = sBracketCounter + 1
VALUE "]"
SET sBracketCounter = sBracketCounter - 1
ENDCASE
ENDDO
IF sBracketCounter = 0
SET zOK = "OK"
ENDIF
RETURN zOK
ENDFUNCTION- Output:
bBRACKETS_MATCH("[][][][][][][[[[[]]]]]") = "OK"
bBRACKETS_MATCH("sdapasd[a]dfa[fdf][f]a[era[d]as[a]sd[as][da]s[") = "NOT OK"
bBRACKETS_MATCH("3r acwf4[a][ a]sg5s]4t[5e4][taw][ra][r] c[ra]2[r]") = "NOT OK"
bBRACKETS_MATCH("234 rq4ctac3rc[q2 ]r[q4tq4 ]t[4v5 y7 [e6y[]a[45 rv[2q]5q[2q3") = "NOT OK"
Ada
brackets.adb:
with Ada.Numerics.Discrete_Random;
with Ada.Text_IO;
with Ada.Strings.Fixed;
procedure Brackets is
package Random_Positive is new Ada.Numerics.Discrete_Random (Positive);
Positive_Generator : Random_Positive.Generator;
procedure Swap (Left, Right : in out Character) is
Temp : constant Character := Left;
begin
Left := Right;
Right := Temp;
end Swap;
function Generate_Brackets (Bracket_Count : Natural;
Opening_Bracket : Character := '[';
Closing_Bracket : Character := ']')
return String is
use Ada.Strings.Fixed;
All_Brackets : String := Bracket_Count * Opening_Bracket & Bracket_Count * Closing_Bracket;
begin
for I in All_Brackets'Range loop
Swap (All_Brackets (I), All_Brackets (Random_Positive.Random (Positive_Generator) mod (Bracket_Count * 2) + 1));
end loop;
return All_Brackets;
end Generate_Brackets;
function Check_Brackets (Test : String;
Opening_Bracket : Character := '[';
Closing_Bracket : Character := ']')
return Boolean is
Open : Natural := 0;
begin
for I in Test'Range loop
if Test (I) = Opening_Bracket then
Open := Open + 1;
elsif Test (I) = Closing_Bracket then
if Open = 0 then
return False;
else
Open := Open - 1;
end if;
end if;
end loop;
return True;
end Check_Brackets;
begin
Random_Positive.Reset (Positive_Generator);
Ada.Text_IO.Put_Line ("Brackets");
for I in 0 .. 4 loop
for J in 0 .. I loop
declare
My_String : constant String := Generate_Brackets (I);
begin
Ada.Text_IO.Put_Line (My_String & ": " & Boolean'Image (Check_Brackets (My_String)));
end;
end loop;
end loop;
end Brackets;
Output:
Brackets : TRUE []: TRUE ][: FALSE []][: FALSE ][][: FALSE ][][: FALSE [[]]][: FALSE [][][]: TRUE []]][[: FALSE ][][][: FALSE ]]][[[[]: FALSE [[[]][]]: TRUE [][][]][: FALSE [[][]]][: FALSE []]]][[[: FALSE
Aime
unbalanced(data s)
{
integer b, i;
b = i = 0;
while (i + ~s && -1 < b) {
b += s[i -= 1] == '[' ? -1 : 1;
}
b;
}
generate(data b, integer d)
{
if (d) {
d.times(l_bill, list(), -1, '[', ']').l_rand().ucall(b_append, 1, b);
}
}
main(void)
{
integer i;
i = 0;
while (i < 10) {
data s;
generate(s, i);
o_(s, " is ", unbalanced(s) ? "un" : "", "balanced\n");
i += 1;
}
0;
}Sample output:
is balanced ][ is unbalanced ]][[ is unbalanced ]]][[[ is unbalanced [[]][][] is balanced [[][]][][] is balanced []]]][][[][[ is unbalanced ][[[]][[][]]][ is unbalanced [][[[][[]]]]][][ is unbalanced [[][[[[][]]][][]]] is balanced
ALGOL 68
# generates a string of random opening and closing brackets. The number of #
# each type of brackets is speccified in length #
PROC get brackets = ( INT length ) STRING:
BEGIN
INT result length = length * 2;
[ 1 : result length ]CHAR result;
# initialise the brackets to all open brackets #
FOR char pos TO result length DO result[ char pos ] := "[" OD;
# set half of the brackets to close brackets #
INT close count := 0;
WHILE close count < length
DO
INT random pos = 1 + ENTIER ( next random * result length );
IF result[ random pos ] = "["
THEN
close count +:= 1;
result[ random pos ] := "]"
FI
OD;
result
END # get brackets # ;
# returns TRUE if the brackets string contains a correctly nested sequence #
# of brackets, FALSE otherwise #
PROC check brackets = ( STRING brackets ) BOOL:
BEGIN
INT depth := 0;
FOR char pos FROM LWB brackets TO UPB brackets
WHILE
IF brackets[ char pos ] = "["
THEN
depth +:= 1
ELSE
depth -:= 1
FI;
depth >= 0
DO
SKIP
OD;
# depth will be 0 if we reached the end of the string and it was #
# correct, non-0 otherwise #
depth = 0
END # check brackets # ;
# procedure to test check brackets #
PROC test check brackets = ( STRING brackets ) VOID:
print( ( ( brackets
+ ": "
+ IF check brackets( brackets ) THEN "ok" ELSE "not ok" FI
)
, newline
)
) ;
# test the bracket generation and checking PROCs #
test check brackets( get brackets( 0 ) );
FOR length TO 12
DO
TO 2
DO
test check brackets( get brackets( length ) )
OD
OD- Output:
: ok []: ok ][: not ok [][]: ok []][: not ok []]][[: not ok [[]][]: ok ]]][[][[: not ok [[][[]]]: ok [][]]][[][: not ok [[[[]]]][]: ok ]][]]][[[[][: not ok [[[][[[]]]]]: ok [[[]]][[][[]]]: ok [][[][][][][]]: ok []]][][]][[[[]][: not ok ]][]][][[[][][][: not ok ][][]][]][]][[[[[]: not ok ]]][[][][][[[][]][: not ok [[[[][][]][]]][[]]][: not ok ][]][]]][][][][][[[[: not ok ][][]][[][[[[]][][[]]]: not ok ]][[[]][[[[]]]][[[]]][: not ok ]][][]]][]][][]][[[[[[][: not ok ]]][][][]][][[]][[[][][[: not ok
Amazing Hopper
#include <basico.h>
algoritmo
braizq="[", brader="]" // bug de Hopper :(
largo de datos=0
preparar datos (DATA_BRACKET)
obtener tamaño de datos, menos '1', guardar en 'largo de datos'
iterar
bra="", obtener dato, guardar en 'bra'
i=1, b=0, error_pos=""
iterar grupo( ++i, #( i<=len(bra) && is not neg (b) ),\
#( b += ((bra[i]==braizq) - (bra[i]==brader)) )\
#( error_pos = cat(replicate(" ",i-1),"^\n") ) )
solo si ( #(is pos(b)),\
#( error_pos=cat(cat(" ",error_pos),"(missing closed bracket)\n\n")))
solo si ( #(is neg(b)),\
#( error_pos=cat(error_pos,"(extra closed bracket)\n\n")))
imprimir ( #( rpad(" ",40,bra) ), ": ", \
solo si (b, "un"), "balanced\n",\
solo si (b, error_pos) )
mientras ' largo de datos-- '
terminar
subrutinas
DATA_BRACKET:
datos ("","[ [ ] [ [[] ][] ] [[]] ]","[[ ][[[ ][ ]]",\
"[][][[]]][","][[]][] [[[]]] [][]","[][] [][][[]]",\
"[ a-b * [c/d] + [[10 * sin 30 ]-1] ]",\
"[ a-b * [c/d] + [[10 * sin 30 ]]-1] ]")
back
- Output:
: balanced
[ [ ] [ [[] ][] ] [[]] ] : balanced
[[ ][[[ ][ ]] : unbalanced
^
(missing closed bracket)
[][][[]]][ : unbalanced
^
(extra closed bracket)
][[]][] [[[]]] [][] : unbalanced
^
(extra closed bracket)
[][] [][][[]] : balanced
[ a-b * [c/d] + [[10 * sin 30 ]-1] ] : balanced
[ a-b * [c/d] + [[10 * sin 30 ]]-1] ] : unbalanced
^
(extra closed bracket)
ANTLR
Java
grammar balancedBrackets ;
options {
language = Java;
}
bb : {System.out.print("input is: ");} (balancedBrackets {System.out.print($balancedBrackets.text);})* NEWLINE {System.out.println();}
;
balancedBrackets
: OpenBracket balancedBrackets* CloseBracket
;
OpenBracket
: '['
;
CloseBracket
: ']'
;
NEWLINE : '\r'? '\n'
;
Produces:
input is: [] input is: [] ][ input is: line 1:0 missing NEWLINE at ']' [][] input is: [][] ][][ input is: line 1:0 missing NEWLINE at ']' [[][]] input is: [[][]] []][[] input is: []line 1:2 missing NEWLINE at ']'
APL
These are a function to generate a random string of N brackets of each type, and a function to check whether a given string of brackets is balanced.
gen ← (⊂+?+)⍨ ⌷ ('[]'/⍨⊢)
bal ← (((|≡⊢)+\) ∧ 0=+/)(+⌿1 ¯1×[1]'[]'∘.=⊢)
Sample run for 0..N..10:
↑{br←gen ⍵ ⋄ br,': ',(1+bal br)⊃'Bad' 'Good'}¨0,⍳10
: Good
[]: Good
][][: Bad
[][[]]: Good
[]]][[][: Bad
][][[[[]]]: Bad
][][][][][[]: Bad
][[[][[][]][]]: Bad
[[][[]]][[[[]]]]: Good
[[[]][[[[][]][]]]]: Good
]][][][][[][][]][[[]: Bad
AppleScript
(ES6 functionally composed version)
-- CHECK NESTING OF SQUARE BRACKET SEQUENCES ---------------------------------
-- Zero-based index of the first problem (-1 if none found):
-- imbalance :: String -> Integer
on imbalance(strBrackets)
script
on errorIndex(xs, iDepth, iIndex)
set lngChars to length of xs
if lngChars > 0 then
set iNext to iDepth + cond(item 1 of xs = "[", 1, -1)
if iNext < 0 then -- closing bracket unmatched
iIndex
else
if lngChars > 1 then -- continue recursively
errorIndex(items 2 thru -1 of xs, iNext, iIndex + 1)
else -- end of string
cond(iNext = 0, -1, iIndex)
end if
end if
else
cond(iDepth = 0, -1, iIndex)
end if
end errorIndex
end script
result's errorIndex(characters of strBrackets, 0, 0)
end imbalance
-- TEST ----------------------------------------------------------------------
-- Random bracket sequences for testing
-- brackets :: Int -> String
on randomBrackets(n)
-- bracket :: () -> String
script bracket
on |λ|(_)
cond((random number) < 0.5, "[", "]")
end |λ|
end script
intercalate("", map(bracket, enumFromTo(1, n)))
end randomBrackets
on run
set nPairs to 6
-- report :: Int -> String
script report
property strPad : concat(replicate(nPairs * 2 + 4, space))
on |λ|(n)
set w to n * 2
set s to randomBrackets(w)
set i to imbalance(s)
set blnOK to (i = -1)
set strStatus to cond(blnOK, "OK", "problem")
set strLine to "'" & s & "'" & ¬
(items (w + 2) thru -1 of strPad) & strStatus
set strPointer to cond(blnOK, ¬
"", linefeed & concat(replicate(i + 1, space)) & "^")
intercalate("", {strLine, strPointer})
end |λ|
end script
linefeed & ¬
intercalate(linefeed, ¬
map(report, enumFromTo(1, nPairs))) & linefeed
end run
-- GENERIC FUNCTIONS ---------------------------------------------------------
-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map
-- foldl :: (a -> b -> a) -> a -> [b] -> a
on foldl(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from 1 to lng
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldl
-- Text -> [Text] -> Text
on intercalate(strText, lstText)
set {dlm, my text item delimiters} to {my text item delimiters, strText}
set strJoined to lstText as text
set my text item delimiters to dlm
return strJoined
end intercalate
-- concat :: [[a]] -> [a] | [String] -> String
on concat(xs)
script append
on |λ|(a, b)
a & b
end |λ|
end script
if length of xs > 0 and class of (item 1 of xs) is string then
set empty to ""
else
set empty to {}
end if
foldl(append, empty, xs)
end concat
-- Egyptian multiplication - progressively doubling a list, appending
-- stages of doubling to an accumulator where needed for binary
-- assembly of a target length
-- replicate :: Int -> a -> [a]
on replicate(n, a)
set out to {}
if n < 1 then return out
set dbl to {a}
repeat while (n > 1)
if (n mod 2) > 0 then set out to out & dbl
set n to (n div 2)
set dbl to (dbl & dbl)
end repeat
return out & dbl
end replicate
-- Value of one of two expressions
-- cond :: Bool -> a -> b -> c
on cond(bln, f, g)
if bln then
set e to f
else
set e to g
end if
if class of e is handler then
mReturn(e)'s |λ|()
else
e
end if
end cond
-- enumFromTo :: Int -> Int -> [Int]
on enumFromTo(m, n)
if m > n then
set d to -1
else
set d to 1
end if
set lst to {}
repeat with i from m to n by d
set end of lst to i
end repeat
return lst
end enumFromTo
-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn
Sample output:
'][' problem
^
'[][[' problem
^
'[[][]]' OK
'][][[][[' problem
^
'[]][][[][]' problem
^
'[[[][]]]][][' problem
^
ARM Assembly
.data
balanced_message:
.ascii "OK\n"
unbalanced_message:
.ascii "NOT OK\n"
.text
.equ balanced_msg_len, 3
.equ unbalanced_msg_len, 7
BalancedBrackets:
mov r1, #0
mov r2, #0
mov r3, #0
process_bracket:
ldrb r2, [r0, r1]
cmp r2, #0
beq evaluate_balance
cmp r2, #'['
addeq r3, r3, #1
cmp r2, #']'
subeq r3, r3, #1
cmp r3, #0
blt unbalanced
add r1, r1, #1
b process_bracket
evaluate_balance:
cmp r3, #0
beq balanced
unbalanced:
ldr r1, =unbalanced_message
mov r2, #unbalanced_msg_len
b display_result
balanced:
ldr r1, =balanced_message
mov r2, #balanced_msg_len
display_result:
mov r7, #4
mov r0, #1
svc #0
mov pc, lrArturo
isBalanced: function [s][
cnt: 0
loop split s [ch][
if? ch="]" [
cnt: cnt-1
if cnt<0 -> return false
]
else [
if ch="[" -> cnt: cnt+1
]
]
cnt=0
]
loop 1..10 'i [
str: join map 0..(2*i)-1 [x][ sample ["[" "]"]]
prints str
if? isBalanced str -> print " OK"
else -> print " Not OK"
]
- Output:
[] OK [[[] Not OK [][][] OK [[][[]]] OK [[[[[][[]] Not OK [[]][[[]]][] OK ][[]][][[[[[[] Not OK ]][[]]][[[]]][]] Not OK ][[[[[[]]][]]][][] Not OK []][][][]]][[[[][][] Not OK
AutoHotkey
; Generate 10 strings with equal left and right brackets
Loop, 5
{
B = %A_Index%
loop 2
{
String =
Loop % B
String .= "[`n"
Loop % B
String .= "]`n"
Sort, String, Random
StringReplace, String, String,`n,,All
Example .= String " - " IsBalanced(String) "`n"
}
}
MsgBox % Example
return
IsBalanced(Str)
{
Loop, PARSE, Str
{
If A_LoopField = [
i++
Else if A_LoopField = ]
i--
If i < 0
return "NOT OK"
}
Return "OK"
}
Output:
][ - NOT OK ][ - NOT OK [][] - OK [[]] - OK []][[] - NOT OK ]][[[] - NOT OK ][[]][][ - NOT OK [][[[]]] - OK [][]]][[[] - NOT OK [[][[]]][] - OK
A second example repeatedly replacing []:
Loop, 5
{
B = %A_Index%
loop 2
{
String =
Loop % B
String .= "[`n"
Loop % B
String .= "]`n"
Sort, String, Random
StringReplace, String, String,`n,,All
Example .= String " - " IsBalanced(String) "`n"
}
}
MsgBox % Example
return
IsBalanced(Str){
While (Instr(Str,"[]"))
StringReplace, Str, Str,[],,All
Return Str ? "False" : "True"
}
Sample output:
[] - True ][ - False ]][[ - False []][ - False [[]]][ - False ]][[[] - False [][]]][[ - False []][][][ - False [[[][]][]] - True [][][[[]]] - True
AutoIt
#include <Array.au3>
Local $Array[1]
_ArrayAdd($Array, "[]")
_ArrayAdd($Array, "[][]")
_ArrayAdd($Array, "[[][]]")
_ArrayAdd($Array, "][")
_ArrayAdd($Array, "][][")
_ArrayAdd($Array, "[]][[]")
For $i = 0 To UBound($Array) -1
Balanced_Brackets($Array[$i])
If @error Then
ConsoleWrite($Array[$i] &" = NOT OK"&@CRLF)
Else
ConsoleWrite($Array[$i] &" = OK"&@CRLF)
EndIf
Next
Func Balanced_Brackets($String)
Local $cnt = 0
$Split = Stringsplit($String, "")
For $i = 1 To $Split[0]
If $split[$i] = "[" Then $cnt += 1
If $split[$i] = "]" Then $cnt -= 1
If $cnt < 0 Then Return SetError(1,0,0)
Next
Return 1
EndFunc
AWK
#!/usr/bin/awk -f
BEGIN {
print isbb("[]")
print isbb("][")
print isbb("][][")
print isbb("[][]")
print isbb("[][][]")
print isbb("[]][[]")
}
function isbb(x) {
s = 0
for (k=1; k<=length(x); k++) {
c = substr(x,k,1)
if (c=="[") {s++}
else { if (c=="]") s-- }
if (s<0) {return 0}
}
return (s==0)
}
Output:
1 0 0 1 1 0
BaCon
FOR len = 0 TO 18 STEP 2
str$ = ""
DOTIMES len
str$ = str$ & CHR$(IIF(RANDOM(2) = 0, 91, 93))
DONE
status = 0
FOR x = 1 TO LEN(str$)
IF MID$(str$, x, 1) = "[" THEN
INCR status
ELSE
DECR status
FI
IF status < 0 THEN BREAK
NEXT
IF status = 0 THEN
PRINT "OK: ", str$
ELSE
PRINT "BAD: ", str$
ENDIF
NEXT- Output:
OK: OK: [] BAD: ]][] OK: [[]][] OK: [[[][]]] BAD: ][[][]]][] BAD: ]][[]][[[][[ OK: [[][][][][][]] BAD: [[[]]]][[[[[][]] BAD: ][][][][[[[[][]]][
BASIC
DECLARE FUNCTION checkBrackets% (brackets AS STRING)
DECLARE FUNCTION generator$ (length AS INTEGER)
RANDOMIZE TIMER
DO
x$ = generator$ (10)
PRINT x$,
IF checkBrackets(x$) THEN
PRINT "OK"
ELSE
PRINT "NOT OK"
END IF
LOOP WHILE LEN(x$)
FUNCTION checkBrackets% (brackets AS STRING)
'returns -1 (TRUE) if everything's ok, 0 (FALSE) if not
DIM L0 AS INTEGER, sum AS INTEGER
FOR L0 = 1 TO LEN(brackets)
SELECT CASE MID$(brackets, L0, 1)
CASE "["
sum = sum + 1
CASE "]"
sum = sum - 1
END SELECT
IF sum < 0 THEN
checkBrackets% = 0
EXIT FUNCTION
END IF
NEXT
IF 0 = sum THEN
checkBrackets% = -1
ELSE
checkBrackets% = 0
END IF
END FUNCTION
FUNCTION generator$ (length AS INTEGER)
z = INT(RND * length)
IF z < 1 THEN generator$ = "": EXIT FUNCTION
REDIM x(z * 2) AS STRING
FOR i = 0 TO z STEP 2
x(i) = "["
x(i + 1) = "]"
NEXT
FOR i = 1 TO UBOUND(x)
z = INT(RND * 2)
IF z THEN SWAP x(i), x(i - 1)
NEXT
xx$ = ""
FOR i = 0 TO UBOUND(x)
xx$ = xx$ + x(i)
NEXT
generator$ = xx$
END FUNCTION
- Output:
[][[][][]] OK
][[[]] NOT OK
[][] OK
[]][][][[] NOT OK
[][[]][[]] OK
][][[] NOT OK
][[] NOT OK
][][[]][][ NOT OK
][[[][]] NOT OK
][][[[]] NOT OK
][[]][ NOT OK
OK
Applesoft BASIC
The MSX BASIC solution works without any changes.
BASIC256
s$ = "[[]][]"
print s$; " = ";
if not check_brackets(s$) then print "not ";
print "ok"
end
function check_brackets(s$)
level = 0
for i = 1 to length(s$)
c$ = mid(s$, i, 1)
begin case
case c$ = "["
level = level + 1
case c$ = "]"
level = level - 1
if level < 0 then exit for
end case
next i
return level = 0
end functionChipmunk Basic
The MSX BASIC solution works without any changes.
Commodore BASIC
Based on ZX Spectrum BASIC implementation
10 PRINT CHR$(147): REM CLEAR SCREEN
20 FOR N=1 TO 7
30 READ S$
40 IF S$="" THEN PRINT"(EMPTY)";: GOTO 60
50 PRINT S$;
60 PRINT TAB(20);
70 GOSUB 1000
80 NEXT N
90 END
100 REM ********************************
1000 S = 0
1010 FOR K=1 TO LEN(S$)
1020 C$ = MID$(S$,K,1)
1030 IF C$="[" THEN S = S+1
1040 IF C$="]" THEN S = S-1
1050 IF S<0 THEN PRINT "NOT OK": RETURN
1060 NEXT K
1070 IF S=0 THEN PRINT "OK": RETURN
1090 PRINT "NOT OK"
1100 RETURN
2000 DATA , [], ][, [][], ][][, [[][]], []][[]
GW-BASIC
The MSX BASIC solution works without any changes.
MSX Basic
Based on Commodore BASIC implementation
100 CLS : rem 10 HOME for Applesoft BASIC
110 FOR N = 1 TO 7
120 READ S$
130 IF S$ = "" THEN PRINT"(EMPTY)";: GOTO 150
140 PRINT S$;
150 PRINT TAB(9);
160 GOSUB 190
170 NEXT N
180 END
190 S = 0
200 FOR K = 1 TO LEN(S$)
210 C$ = MID$(S$,K,1)
220 IF C$ = "[" THEN S = S+1
230 IF C$ = "]" THEN S = S-1
240 IF S < 0 THEN PRINT "NOT OK": RETURN
250 NEXT K
260 IF S = 0 THEN PRINT " OK": RETURN
270 PRINT "NOT OK"
280 RETURN
290 DATA "", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"
- Output:
(EMPTY) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK
True BASIC
DIM brk$(10)
LET brk$(1) = "[[[][]]]"
LET brk$(2) = "[[[]][[[][[][]]]]]"
LET brk$(3) = "][][]][["
LET brk$(4) = "[][][]"
LET brk$(5) = "[][]][]][[]]][[["
LET brk$(6) = "]][[[[]]]][]]][[[["
LET brk$(7) = "[[][[[]]][]]"
LET brk$(8) = "[]][][][[[]]"
LET brk$(9) = "][]][["
LET brk$(10) = "[]][][][[]"
FOR i = 1 TO 7
LET b$ = brk$(i)
DO WHILE POS(b$,"[]") <> 0
LET x = POS(b$,"[]")
IF x > 0 THEN LET b$ = (b$)[1:x-1] & (b$)[x+2:maxnum]
LOOP
IF TRIM$(b$) = "" THEN
PRINT " OK ";
ELSE
PRINT "Not OK ";
END IF
PRINT brk$(i)
NEXT i
END
uBasic/4tH
@(0) := "[]][][][[]"
@(1) := "[[[][]]]"
@(2) := "[[[]][[[][[][]]]]]"
@(3) := "][][]][["
@(4) := "[][][]"
@(5) := "[][]][]][[]]][[["
@(6) := "]][[[[]]]][]]][[[["
@(7) := "[[][[[]]][]]"
@(8) := "[]][][][[[]]"
@(9) := "][]][["
For x = 0 To 9
Print Using "(_#)";x,Show (@(x));Tab (30);
Do While (Set (a, Find(@(x), "[]")) < 0) = 0
@(x) = Join (Clip (@(x), Len (@(x)) - a), Chop (@(x), a + 2))
Loop
Print "is";Show (Iif (Len (@(x))," not "," "));"balanced"
Next
- Output:
( 0) []][][][[] is not balanced ( 1) [[[][]]] is balanced ( 2) [[[]][[[][[][]]]]] is balanced ( 3) ][][]][[ is not balanced ( 4) [][][] is balanced ( 5) [][]][]][[]]][[[ is not balanced ( 6) ]][[[[]]]][]]][[[[ is not balanced ( 7) [[][[[]]][]] is balanced ( 8) []][][][[[]] is not balanced ( 9) ][]][[ is not balanced 0 OK, 0:472
Batch File
Uses the rewrite rule "[]" -> null to check if brackets are balanced.
:: Balanced Brackets Task from Rosetta Code
:: Batch File Implementation
@echo off
setlocal enabledelayedexpansion
set "num_pairs=10"
set "num_strings=10"
:: the main thing
for /l %%s in (1, 1, %num_strings%) do (
call :generate
call :check
)
echo(
pause
exit /b 0
:: generate strings of brackets
:generate
set "string="
rem put %num_pairs% number of "[" in string
for /l %%c in (1, 1, %num_pairs%) do set "string=!string!["
rem put %num_pairs% number of "]" in random spots of string
set "ctr=%num_pairs%"
for /l %%c in (1, 1, %num_pairs%) do (
set /a "rnd=!random! %% (!ctr! + 1)"
for %%x in (!rnd!) do (
set "left=!string:~0,%%x!"
set "right=!string:~%%x!"
)
set "string=!left!]!right!"
set /a "ctr+=1"
)
goto :EOF
:: check for balance
:check
set "new=%string%"
:check_loop
if "%new%" equ "" (
echo(
echo(%string% is Balanced.
goto :EOF
) else if "%old%" equ "%new%" ( %== unchangeable already? ==%
echo(
echo(%string% is NOT Balanced.
goto :EOF
)
rem apply rewrite rule "[]" -> null
set "old=%new%"
set "new=%old:[]=%"
goto check_loop
- Output:
[][][[[[]]][]]]][[][ is NOT Balanced. ][[]][][][[]]][[[[]] is NOT Balanced. [[[][]][][]][[][][]] is Balanced. ][[[[[]]][][][][][]] is NOT Balanced. ]][][[][]]]][]][[[[[ is NOT Balanced. [[[][[][][[]]]][][]] is Balanced. ][]]][[]][[][[][[]][ is NOT Balanced. [[[][[][]][[[]]][]]] is Balanced. ]][]]][[[][]][[][[[] is NOT Balanced. ][[]][][[]][][]][[][ is NOT Balanced. Press any key to continue . . .
BBC BASIC
FOR x%=1 TO 10
test$=FNgenerate(RND(10))
PRINT "Bracket string ";test$;" is ";FNvalid(test$)
NEXT x%
END
:
DEFFNgenerate(n%)
LOCAL l%,r%,t%,output$
WHILE l%<n% AND r%<n%
CASE RND(2) OF
WHEN 1:
l%+=1
output$+="["
WHEN 2:
r%+=1
output$+="]"
ENDCASE
ENDWHILE
IF l%=n% THEN output$+=STRING$(n%-r%,"]") ELSE output$+=STRING$(n%-l%,"[")
=output$
:
DEFFNvalid(q$)
LOCAL x%,count%
IF LEN(q$)=0 THEN ="OK."
FOR x%=1 TO LEN(q$)
IF MID$(q$,x%,1)="[" THEN count%+=1 ELSE count%-=1
IF count%<0 THEN ="not OK."
NEXT x%
="OK."
Bracket string [[[][]]] is OK. Bracket string [[[]][[[][[][]]]]] is OK. Bracket string ][][]][[ is not OK. Bracket string [][][] is OK. Bracket string [][]][]][[]]][[[ is not OK. Bracket string ]][[[[]]]][]]][[[[ is not OK. Bracket string [[][[[]]][]] is OK. Bracket string []][][][[[]] is not OK. Bracket string ][]][[ is not OK. Bracket string []][][][[] is not OK.
Befunge
This code implements the second part of the task: it reads from standard input an arbitrary string of opening and closing brackets, and checks whether it's balanced or not.
v > "KO TON" ,,,,,, v
> ~ : 25*- #v_ $ | > 25*, @
> "KO" ,, ^
> : 1991+*+- #v_ v
> \ : 1991+*+- #v_v
\ $
^ < <$<
BQN
Balanced brackets are a monoid with the following presentation:
⟨l, r | l·r = e⟩
This allows for a particular simple implementation:
Gen ← (•rand.Deal⊏⥊⟜"[]") 2⊸×
Bal ← {
Mul ← {a‿b𝕊x‿y: ⟨a+0⌈x-b, y+0⌈b-x⟩}
0‿0 ≡ 0‿0("]["⊸=⊸Mul)´𝕩
}
- Output:
(⊢≍Bal¨) Gen¨5⥊3
┌─
╵ "]][][[" "[][][]" "][][[]" "[[][]]" "][[][]"
0 1 0 1 0
┘
Bracmat
Bracmat has no 'random' function, so the shuffle is a bit improvised. A variable someNumber is initialised with a big number is repeatedly divided by the number of '['s in the test string until zero. The remainders are used as index to partition and swap the first half of the test string. Then the second half and first half are also swapped. The test whether the test string is balanced is simple, but not very efficient.
( (bal=|"[" !bal "]" !bal)
& ( generate
= a j m n z N S someNumber
. !arg:<1&
| 11^123+13^666+17^321:?someNumber
& (!arg:?n)+1:?N
& :?S
& whl
' (!n+-1:~<0:?n&"[" "]" !S:?S)
& whl
' ( !someNumber:>0
& mod$(!someNumber.!N):?j
& div$(!someNumber.!N):?someNumber
& !S:?a [!j ?m [!N ?z
& !z !m !a:?S
)
& !S
)
& 0:?L
& whl
' ( generate$!L:?S
& put$(str$(!S ":"))
& out
$ (!S:!bal&Balanced|"Not balanced")
& !L+1:<11:?L
)
);Output:
:Balanced ][:Not balanced [][]:Balanced [][[]]:Balanced [[[]]]][:Not balanced ]]]][][[[[:Not balanced [[][[[]]][]]:Balanced [][]][]]]][[[[:Not balanced [][]][[[]]][][][:Not balanced [][[[[]][]]][[[]]]:Balanced [][[][]][]]][][[[]][:Not balanced
Brat
string.prototype.balanced? = {
brackets = []
balanced = true
my.dice.each_while { c |
true? c == "["
{ brackets << c }
{ true? c == "]"
{ last = brackets.pop
false? last == "["
{ balanced = false }
}
}
balanced
}
true? brackets.empty?
{ balanced }
{ false }
}
generate_brackets = { n | (n.of("[") + n.of("]")).shuffle.join }
1.to 10 { n |
test = generate_brackets n
true? test.balanced?
{ p "#{test} is balanced" }
{ p "#{test} is not balanced" }
}Output:
[] is balanced ][][ is not balanced [[]][] is balanced [[[]][]] is balanced [[[[]]]]][ is not balanced ][[][]][[[]] is not balanced ]][[][][[]][][ is not balanced [[[][[]]][][][]] is balanced ][]][]]]][][[[][[[ is not balanced ][[[[][][][[][][]]]] is not balanced
C
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int isBal(const char*s,int l){
signed c=0;
while(l--)
if(s[l]==']') ++c;
else if(s[l]=='[') if(--c<0) break;
return !c;
}
void shuffle(char*s,int h){
int x,t,i=h;
while(i--){
t=s[x=rand()%h];
s[x]=s[i];
s[i]=t;
}
}
void genSeq(char*s,int n){
if(n){
memset(s,'[',n);
memset(s+n,']',n);
shuffle(s,n*2);
}
s[n*2]=0;
}
void doSeq(int n){
char s[64];
const char *o="False";
genSeq(s,n);
if(isBal(s,n*2)) o="True";
printf("'%s': %s\n",s,o);
}
int main(){
int n=0;
while(n<9) doSeq(n++);
return 0;
}
result:
'': True
'[]': True
']][[': False
'[][][]': True
'[]][[]][': False
'[]][[[[]]]': False
']]]][[[]][[[': False
']]]]]][][[[[[[': False
'[][]][[][[[]]][]': False
C#
using System;
using System.Linq;
class Program
{
static bool IsBalanced(string text, char open = '[', char close = ']')
{
var level = 0;
foreach (var character in text)
{
if (character == close)
{
if (level == 0)
{
return false;
}
level--;
}
if (character == open)
{
level++;
}
}
return level == 0;
}
static string RandomBrackets(int count, char open = '[', char close = ']')
{
var random = new Random();
return string.Join(string.Empty,
(new string(open, count) + new string(close, count)).OrderBy(c => random.Next()));
}
static void Main()
{
for (var count = 0; count < 9; count++)
{
var text = RandomBrackets(count);
Console.WriteLine("\"{0}\" is {1}balanced.", text, IsBalanced(text) ? string.Empty : "not ");
}
}
}
Sample output:
"" is balanced. "[]" is balanced. "[]][" is not balanced. "[][][]" is balanced. "[[[]][]]" is balanced. "[][[][[]]]" is balanced. "[]][][][[][]" is not balanced. "[]]][][]][[][[" is not balanced. "[]]][]]][[][[][[" is not balanced.
// simple solution
string input = Console.ReadLine();
if (input.Length % 2 != 0)
{
Console.WriteLine("Not Okay");
return;
}
for (int i = 0; i < input.Length; i++)
{
if (i < input.Length - 1)
{
if (input[i] == '[' && input[i + 1] == ']')
{
input = input.Remove(i, 2);
i = -1;
}
}
}
if (input.Length == 0)
Console.WriteLine("Okay");
else
Console.WriteLine("Not Okay");
C++
#include <algorithm>
#include <iostream>
#include <string>
std::string generate(int n, char left = '[', char right = ']')
{
std::string str(std::string(n, left) + std::string(n, right));
std::random_shuffle(str.begin(), str.end());
return str;
}
bool balanced(const std::string &str, char left = '[', char right = ']')
{
int count = 0;
for (std::string::const_iterator it = str.begin(); it != str.end(); ++it)
{
if (*it == left)
count++;
else if (*it == right)
if (--count < 0) return false;
}
return count == 0;
}
int main()
{
srand(time(NULL)); // seed rng
for (int i = 0; i < 9; ++i)
{
std::string s(generate(i));
std::cout << (balanced(s) ? " ok: " : "bad: ") << s << "\n";
}
}
Output:
ok: ok: [] ok: [][] bad: []][[] ok: [[[]][]] bad: ][[[[]][]] ok: [[[]][[]][]] bad: ]][[]][[[[][]] bad: [[]]]][]][[][[[]
Ceylon
import com.vasileff.ceylon.random.api {
platformRandom,
Random
}
"""Run the example code for Rosetta Code ["Balanced brackets" task] (http://rosettacode.org/wiki/Balanced_brackets)."""
shared void run() {
value rnd = platformRandom();
for (len in (0..10)) {
value c = generate(rnd, len);
print("``c.padTrailing(20)`` - ``if (balanced(c)) then "OK" else "NOT OK" ``");
}
}
String generate(Random rnd, Integer count)
=> if (count == 0) then ""
else let(length = 2*count,
brackets = zipEntries(rnd.integers(length).take(length),
"[]".repeat(count))
.sort((a,b) => a.key<=>b.key)
.map(Entry.item))
String(brackets);
Boolean balanced(String input)
=> let (value ints = { for (c in input) if (c == '[') then 1 else -1 })
ints.filter((i) => i != 0)
.scan(0)(plus<Integer>)
.every((i) => i >= 0);
Output:
- OK [] - OK ][[] - NOT OK ][[]][ - NOT OK []]][[][ - NOT OK [[[][][]]] - OK [[][]][[]][] - OK [[][[[]]][]][] - OK ]][[][][[][]][[] - NOT OK [[]]]]]]][[[[][][[ - NOT OK [[]][[]][[]]]][[[]][ - NOT OK
Clojure
(defn gen-brackets [n]
(->> (concat (repeat n \[) (repeat n \]))
shuffle
(apply str ,)))
(defn balanced? [s]
(loop [[first & coll] (seq s)
stack '()]
(if first
(if (= first \[)
(recur coll (conj stack \[))
(when (= (peek stack) \[)
(recur coll (pop stack))))
(zero? (count stack)))))
There are other ways to express the balanced? function.
- We can use
reduceto consume the sequence:
(defn balanced? [s] (empty? (reduce (fn [stack first] (case first \[ (conj stack \[) \] (if (seq stack) (pop stack) (reduced [:UNDERFLOW])))) '() s)))
- Only
[s are put on the stack. We can just count the unmatched ones.
(defn balanced? [s] (let [opens-closes (->> s (map {\[ 1, \] -1}) (reductions + 0))] (and (not-any? neg? opens-closes) (zero? (last opens-closes)))))
Output:
user> (->> (range 10)
(map gen-brackets ,)
(map (juxt identity balanced?) ,)
vec)
[["" true]
["[]" true]
["[[]]" true]
["[][[]]" true]
["[]][][][" nil]
["[[[[[]]]]]" true]
["]][[][][[[]]" nil]
["[]]]][[[[]][][" nil]
["][][[]]][[][][][" nil]
["][][]]][]][[[][[[]" nil]
CLU
% This program needs the random number generator from
% "misc.lib" that comes with PCLU.
shuffle = proc [T: type] (a: array[t])
aT = array[t]
for i: int in int$from_to_by(aT$size(a)-1,0,-1) do
x: int := aT$low(a) + i
y: int := aT$low(a) + random$next(i+1)
temp: T := a[x]
a[x] := a[y]
a[y] := temp
end
end shuffle
brackets = proc (n: int) returns (string)
br: array[char] := array[char]$[]
for i: int in int$from_to(1,2*n) do
if i<=n then array[char]$addh(br, '[')
else array[char]$addh(br, ']')
end
end
shuffle[char](br)
return(string$ac2s(br))
end brackets
balanced = proc (br: string) returns (bool)
depth: int := 0
for c: char in string$chars(br) do
if c='[' then depth := depth + 1
elseif c=']' then depth := depth - 1
end
if depth<0 then return(false) end
end
return(depth = 0)
end balanced
start_up = proc ()
po: stream := stream$primary_output()
d: date := now()
random$seed(d.second + 60*(d.minute + 60*d.hour))
for size: int in int$from_to(0, 10) do
b: string := brackets(size)
stream$puts(po, "\"" || b || "\": ")
if balanced(b) then
stream$putl(po, "balanced")
else
stream$putl(po, "not balanced")
end
end
end start_up- Output:
"": balanced "[]": balanced "[][]": balanced "[[]][]": balanced "[[]][[]]": balanced "][[]][][[]": not balanced "[][][]][]][[": not balanced "][]][]]][][[[[": not balanced "[][[]][][][[[]]]": balanced "][[][][]][[]][][[]": not balanced "]]]][[[[]][][][[][[]": not balanced
COBOL
IDENTIFICATION DIVISION.
PROGRAM-ID. test-balanced-brackets.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 True-Val CONSTANT 0.
01 False-Val CONSTANT 1.
LOCAL-STORAGE SECTION.
01 current-time PIC 9(10).
01 bracket-type PIC 9.
88 add-open-bracket VALUE 1.
01 bracket-string-area.
03 bracket-string PIC X(10) OCCURS 10 TIMES.
01 i PIC 999.
01 j PIC 999.
PROCEDURE DIVISION.
*> Seed RANDOM().
MOVE FUNCTION CURRENT-DATE (7:10) TO current-time
MOVE FUNCTION RANDOM(current-time) TO current-time
*> Generate random strings of brackets.
PERFORM VARYING i FROM 1 BY 1 UNTIL 10 < i
PERFORM VARYING j FROM 1 BY 1 UNTIL i < j
COMPUTE bracket-type =
FUNCTION REM(FUNCTION RANDOM * 1000, 2)
IF add-open-bracket
MOVE "[" TO bracket-string (i) (j:1)
ELSE
MOVE "]" TO bracket-string (i) (j:1)
END-IF
END-PERFORM
END-PERFORM
*> Display if the strings are balanced or not.
PERFORM VARYING i FROM 1 BY 1 UNTIL 10 < i
CALL "check-if-balanced" USING bracket-string (i)
IF RETURN-CODE = True-Val
DISPLAY FUNCTION TRIM(bracket-string (i))
" is balanced."
ELSE
DISPLAY FUNCTION TRIM(bracket-string (i))
" is not balanced."
END-IF
END-PERFORM
GOBACK
.
END PROGRAM test-balanced-brackets.
IDENTIFICATION DIVISION.
PROGRAM-ID. check-if-balanced.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 True-Val CONSTANT 0.
01 False-Val CONSTANT 1.
LOCAL-STORAGE SECTION.
01 nesting-level PIC S999.
01 i PIC 999.
LINKAGE SECTION.
01 bracket-string PIC X(100).
PROCEDURE DIVISION USING bracket-string.
PERFORM VARYING i FROM 1 BY 1
UNTIL (100 < i)
OR (bracket-string (i:1) = SPACE)
OR (nesting-level < 0)
IF bracket-string (i:1) = "["
ADD 1 TO nesting-level
ELSE
SUBTRACT 1 FROM nesting-level
IF nesting-level < 0
MOVE False-Val TO RETURN-CODE
GOBACK
END-IF
END-IF
END-PERFORM
IF nesting-level = 0
MOVE True-Val TO RETURN-CODE
ELSE
MOVE False-Val TO RETURN-CODE
END-IF
GOBACK
.
END PROGRAM check-if-balanced.
CoffeeScript
isBalanced = (brackets) ->
openCount = 0
for bracket in brackets
openCount += if bracket is '[' then 1 else -1
return false if openCount < 0
openCount is 0
bracketsCombinations = (n) ->
for i in [0...Math.pow 2, n]
str = i.toString 2
str = '0' + str while str.length < n
str.replace(/0/g, '[').replace(/1/g, ']')
for brackets in bracketsCombinations 4
console.log brackets, isBalanced brackets
output
> coffee balanced.coffee
[[[[ false
[[[] false
[[][ false
[[]] true
[][[ false
[][] true
[]][ false
[]]] false
][[[ false
][[] false
][][ false
][]] false
]][[ false
]][] false
]]][ false
]]]] false
Common Lisp
(defun string-of-brackets (n)
(let* ((len (* 2 n))
(res (make-string len))
(opening (/ len 2))
(closing (/ len 2)))
(dotimes (i len res)
(setf (aref res i)
(cond ((zerop opening) #\])
((zerop closing) #\[)
(t (if (= (random 2) 0)
(progn (decf opening) #\[)
(progn (decf closing) #\]))))))))
(defun balancedp (string)
(zerop (reduce (lambda (nesting bracket)
(ecase bracket
(#\] (if (= nesting 0)
(return-from balancedp nil)
(1- nesting)))
(#\[ (1+ nesting))))
string
:initial-value 0)))
(defun show-balanced-brackets ()
(dotimes (i 10)
(let ((s (string-of-brackets i)))
(format t "~3A: ~A~%" (balancedp s) s))))
Output:
CL-USER> (show-balanced-brackets) T : NIL: ][ T : [[]] NIL: []]][[ T : [][][][] NIL: []][]][[[] NIL: []]]]][][[[[ NIL: ][]]]]][[[[][[ T : [[[[[[][[]]]]]]] NIL: ]][[[[][]][[[[]]]]
Component Pascal
BlackBox Component Builder
MODULE Brackets;
IMPORT StdLog, Args, Stacks (* See Task Stacks *);
TYPE
Character = POINTER TO RECORD (Stacks.Object)
c: CHAR
END;
PROCEDURE NewCharacter(c: CHAR): Character;
VAR
n: Character;
BEGIN
NEW(n);n.c:= c;RETURN n
END NewCharacter;
PROCEDURE (c: Character) Show*;
BEGIN
StdLog.String("Character(");StdLog.Char(c.c);StdLog.String(");");StdLog.Ln
END Show;
PROCEDURE CheckBalance(str: ARRAY OF CHAR): BOOLEAN;
VAR
s: Stacks.Stack;
n,x: ANYPTR;
i: INTEGER;
c : CHAR;
BEGIN
i := 0; s := Stacks.NewStack();
WHILE (i < LEN(str$)) & (~Args.IsBlank(str[i])) & (str[i] # 0X) DO
IF s.Empty() THEN
s.Push(NewCharacter(str[i]));
ELSE
n := s.top.data;
WITH
n : Character DO
IF (str[i] = ']')& (n.c = '[') THEN
x := s.Pop();
ELSE
s.Push(NewCharacter(str[i]))
END;
ELSE RETURN FALSE;
END;
END;
INC(i)
END;
RETURN s.Empty();
END CheckBalance;
PROCEDURE Do*;
VAR
p : Args.Params;
i: INTEGER;
BEGIN
Args.Get(p); (* Get Params *)
FOR i := 0 TO p.argc - 1 DO
StdLog.String(p.args[i] + ":>");StdLog.Bool(CheckBalance(p.args[i]));StdLog.Ln
END
END Do;
END Brackets.
Execute: ^Q Brackets.Do [] [][] [[][]] ][ ][][ []][[]~
Output:
[] :> $TRUE [][] :> $TRUE [[][]] :> $TRUE ][ :> $FALSE ][][ :> $FALSE []][[]:> $FALSE
Crystal
def generate(n : Int)
(['[',']'] * n).shuffle.join # Implicit return
end
def is_balanced(str : String)
count = 0
str.each_char do |ch|
case ch
when '['
count += 1
when ']'
count -= 1
if count < 0
return false
end
else
return false
end
end
count == 0
end
10.times do |i|
str = generate(i)
puts "#{str}: #{is_balanced(str)}"
end
Output:
: true []: true ][][: false ][[]][: false []]][][[: false ][[]][[[]]: false []]][[[]][[]: false [[][[[][]]]]][: false [[[]]]][][][][[]: false [[][][]][][[]][][]: true
D
Standard Version
D standard library has a function for this.
import std.stdio, std.algorithm, std.random, std.range;
void main() {
foreach (immutable i; 1 .. 9) {
immutable s = iota(i * 2).map!(_ => "[]"[uniform(0, 2)]).array;
writeln(s.balancedParens('[', ']') ? " OK: " : "bad: ", s);
}
}
- Output:
OK: [] bad: []][ OK: [][][] bad: [][]]][[ OK: [[[]][]][] bad: ][][[[][][]] bad: [[]][[]]]]][[[ bad: ][]]][[[[][][][]
Imperative Version
import std.stdio, std.random, std.range, std.algorithm;
bool isBalanced(in string txt) pure nothrow {
auto count = 0;
foreach (immutable c; txt) {
if (c == ']') {
count--;
if (count < 0)
return false;
} else if (c == '[')
count++;
}
return count == 0;
}
void main() {
foreach (immutable i; 1 .. 9) {
immutable s = iota(i * 2).map!(_ => "[]"[uniform(0, 2)]).array;
writeln(s.isBalanced ? " OK " : "Bad ", s);
}
}
The output is similar.
Functional Style
import std.stdio, std.random, std.range, std.algorithm;
bool isBalanced(in string s, in char[2] pars="[]") pure nothrow @safe @nogc {
bool bal(in string t, in int nb = 0) pure nothrow @safe @nogc {
if (!nb && t.empty) return true;
if (t.empty || nb < 0) return false;
if (t[0] == pars[0]) return bal(t.dropOne, nb + 1);
if (t[0] == pars[1]) return bal(t.dropOne, nb - 1);
return bal(t.dropOne, nb); // Ignore char.
}
return bal(s);
}
void main() {
foreach (immutable i; 1 .. 9) {
immutable s = iota(i * 2).map!(_ => "[]"[uniform(0, $)]).array;
writeln(s.isBalanced ? " OK " : "Bad ", s);
}
}
Delphi
procedure Balanced_Brackets;
var BracketsStr : string;
TmpStr : string;
I,J : integer;
begin
Randomize;
for I := 1 to 9 do
begin
{ Create a random string of 2*N chars with N*"[" and N*"]" }
TmpStr := '';
for J := 1 to I do
TmpStr := '['+TmpStr+']';
BracketsStr := '';
while TmpStr > '' do
begin
J := Random(Length(TmpStr))+1;
BracketsStr := BracketsStr+TmpStr[J];
Delete(TmpStr,J,1);
end;
TmpStr := BracketsStr;
{ Test for balanced brackets }
while Pos('[]',TmpStr) > 0 do
Delete(TmpStr,Pos('[]',TmpStr),2);
if TmpStr = '' then
writeln(BracketsStr+': OK')
else
writeln(BracketsStr+': not OK');
end;
end;
[]: OK [[]]: OK [][][]: OK [[[]][]]: OK ]]]][[[[[]: not OK ][[][][[[]]]: not OK [][[]]][[][[]]: not OK [[[[[]][]][[]]]]: OK []]][][[[[[]][]][]: not OK
Déjà Vu
matching?:
swap 0
for c in chars:
if = c "]":
++
elseif = c "[":
if not dup:
drop
return false
--
not
!. matching? ""
!. matching? "[]"
!. matching? "[][]"
!. matching? "[[][]]"
!. matching? "]["
!. matching? "][]["
!. matching? "[]][[]"- Output:
true true true true false false false
EasyLang
func balanced code$ .
for i to len code$
h$ = substr code$ i 1
if h$ = "["
br += 1
elif h$ = "]"
br -= 1
.
if br < 0
return 0
.
.
return if br = 0
.
repeat
inp$ = input
until inp$ = "eof"
print inp$ & "\t" & balanced inp$
.
#
input_data
[]
[][]
[[][]]
][
][][
[]][[]
eof
EchoLisp
(define (balance str)
(for/fold (closed 0) ((par str))
#:break (< closed 0 ) => closed
(+ closed
(cond
((string=? par "[") 1)
((string=? par "]") -1)
(else 0)))))
(define (task N)
(define str (list->string (append (make-list N "[") (make-list N "]"))))
(for ((i 10))
(set! str (list->string (shuffle (string->list str))))
(writeln (if (zero? (balance str)) '👍 '❌ ) str)))
(task 4)
❌ "[]]][[]["
❌ "]][][[[]"
❌ "][[[]]]["
👍 "[][[[]]]"
❌ "]][[][]["
❌ "][][[[]]"
👍 "[][][[]]"
❌ "]][[][[]"
❌ "[[]]][[]"
❌ "[[][]]]["
Ecstasy
module BalancedBrackets {
Boolean balanced(String text) {
Int depth = 0;
for (Char ch : text) {
switch (ch, depth) {
case ('[', _):
++depth;
break;
case (']', 0):
return False;
case (']', _):
--depth;
break;
}
}
return depth==0;
}
@Inject Console console;
void run() {
String[] tests =
[
"[]",
"[][]",
"[]][[]",
"[[[]][]]",
"][[[[]][]]",
"[[[]][[]][]]",
"]][[]][[[[][]]",
"[[]]]][]][[][[[]",
];
Int longest = tests.map(s -> s.size).reduce(0, (max, len) -> max.maxOf(len));
for (String test : tests) {
console.print($"{test}{' ' * (longest-test.size)} {balanced(test) ? "OK" : "NOT OK"}");
}
}
}
- Output:
[] OK [][] OK []][[] NOT OK [[[]][]] OK ][[[[]][]] NOT OK [[[]][[]][]] OK ]][[]][[[[][]] NOT OK [[]]]][]][[][[[] NOT OK
ed
Balanced brackets can be recursively defined as:
- A pair of brackets [] is balanced.
- An expression wrapped in matching brackets and containing balanced brackets expressions is balanced.
Based on that, the logic might be: if we remove the innermost balanced brackets, then the ones around them turn into simple matching brackets. Repeat recursively/iteratively, and a proper balanced set of brackets reduces to empty string. Unbalanced brackets don't, because they stop matching the [] part at some moment.
# by Artyom Bologov
H
# Remove all the non-bracket chars
g/.*/s/[^][]//gp
# Repeatedly remove all the simple matching brackets.
# Add more lines to handle deeper nested expressions.
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/\[\]/s///g
g/./s/.*/Not balanced!/
g/^$/s/.*/Balanced!/
,p
Q
- Output:
Notice that the script doesn't generate bracket expressions. That's because ed has no built-in Random Number Generator and any reliable ways to generate chaos. Still, it's good at recognizing patterns in input. That's why the example input is used here to test the algo.
$ ed -s balanced-brackets.input < balanced-brackets.ed Newline appended [] [][] [[][]] ][ ][][ []][[] Balanced! Balanced! Balanced! Balanced! Not balanced! Not balanced! Not balanced!
Elena
ELENA 6.x :
// Generate a string with N opening brackets ("[") and N closing brackets ("]"), in some arbitrary order.
// Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order),
// none of which mis-nest.
import system'routines;
import extensions;
import extensions'text;
randomBrackets(len)
{
if (0 == len)
{
^emptyString
}
else
{
var brackets :=
Array.allocate(len).populate::(i => $91)
+
Array.allocate(len).populate::(i => $93);
brackets := brackets.randomize(len * 2);
^ brackets.summarize(new StringWriter()).toString()
}
}
extension op
{
get isBalanced()
{
var counter := new Integer(0);
self.seekEach::(ch => counter.append((ch==$91).iif(1,-1)) < 0);
^ (0 == counter)
}
}
public program()
{
for(int len := 0; len < 9; len += 1)
{
var str := randomBrackets(len);
console.printLine("""",str,"""",str.isBalanced ? " is balanced" : " is not balanced")
};
console.readChar()
}- Output:
"" is balanced "[]" is balanced "][[]" is not balanced "[[[]]]" is balanced "][[[]]][" is not balanced "[]]]][[[][" is not balanced "[[]][][[]]][" is not balanced "[][]]]]][[[[][" is not balanced "][]]][[[[][[][]]" is not balanced "][]][][[]]][[[]][[" is not balanced
Elixir
defmodule Balanced_brackets do
def task do
Enum.each(0..5, fn n ->
brackets = generate(n)
result = is_balanced(brackets) |> task_balanced
IO.puts "#{brackets} is #{result}"
end)
end
defp generate( 0 ), do: []
defp generate( n ) do
for _ <- 1..2*n, do: Enum.random ["[", "]"]
end
def is_balanced( brackets ), do: is_balanced_loop( brackets, 0 )
defp is_balanced_loop( _, n ) when n < 0, do: false
defp is_balanced_loop( [], 0 ), do: true
defp is_balanced_loop( [], _n ), do: false
defp is_balanced_loop( ["[" | t], n ), do: is_balanced_loop( t, n + 1 )
defp is_balanced_loop( ["]" | t], n ), do: is_balanced_loop( t, n - 1 )
defp task_balanced( true ), do: "OK"
defp task_balanced( false ), do: "NOT OK"
end
Balanced_brackets.task
- Output:
is OK [[ is NOT OK [][] is OK ]][]][ is NOT OK [[][][]] is OK [][[][[]]] is OK
Erlang
-module( balanced_brackets ).
-export( [generate/1, is_balanced/1, task/0] ).
generate( N ) ->
[generate_bracket(random:uniform()) || _X <- lists:seq(1, 2*N)].
is_balanced( String ) -> is_balanced_loop( String, 0 ).
task() ->
lists:foreach( fun (N) ->
String = generate( N ),
Result = is_balanced( String ),
io:fwrite( "~s is ~s~n", [String, task_balanced(Result)] )
end,
lists:seq(0, 5) ).
is_balanced_loop( _String, N ) when N < 0 -> false;
is_balanced_loop( [], 0 ) -> true;
is_balanced_loop( [], _N ) -> false;
is_balanced_loop( [$[ | T], N ) -> is_balanced_loop( T, N + 1 );
is_balanced_loop( [$] | T], N ) -> is_balanced_loop( T, N - 1 ).
generate_bracket( N ) when N =< 0.5 -> $[;
generate_bracket( N ) when N > 0.5 -> $].
task_balanced( true ) -> "OK";
task_balanced( false ) -> "NOT OK".
- Output:
47> balanced_brackets:task(). is OK [[ is NOT OK [][] is OK [[[[][ is NOT OK []]]]][[ is NOT OK [[[][[[[]] is NOT OK
Euphoria
function check_brackets(sequence s)
integer level
level = 0
for i = 1 to length(s) do
if s[i] = '[' then
level += 1
elsif s[i] = ']' then
level -= 1
if level < 0 then
return 0
end if
end if
end for
return level = 0
end function
function generate_brackets(integer n)
integer opened,closed,r
sequence s
opened = n
closed = n
s = ""
for i = 1 to n*2 do
r = rand(opened+closed)
if r<=opened then
s &= '['
opened -= 1
else
s &= ']'
closed -= 1
end if
end for
return s
end function
sequence s
for i = 1 to 10 do
s = generate_brackets(3)
puts(1,s)
if check_brackets(s) then
puts(1," OK\n")
else
puts(1," NOT OK\n")
end if
end forSample output:
]]][[[ NOT OK [[[]]] OK [[]][] OK [][][] OK ]][[][ NOT OK [][[]] OK [[[]]] OK [[]][] OK []]][[ NOT OK [][[]] OK
Excel
LAMBDA
Binding the names bracketReport and testRandomBrackets to the following lambda expressions in the Name Manager of the Excel WorkBook, together with names for their helper functions:
(See LAMBDA: The ultimate Excel worksheet function)
bracketReport
=LAMBDA(bracketPair,
LAMBDA(s,
LET(
depths, SCANLCOLS(
LAMBDA(depth, charDelta,
depth + charDelta
)
)(0)(
codesFromBrackets(bracketPair)(
MID(s,
SEQUENCE(1, LEN(s), 1, 1),
1
)
)
),
overClosePosn, IFNA(MATCH(-1, depths, 0), 0),
IF(0 <> overClosePosn,
"Overclosed at char " & (overClosePosn - 1),
IF(0 <> LASTCOL(depths),
"Underclosed by end",
"OK"
)
)
)
)
)
testRandomBrackets
=LAMBDA(bracketPair,
LAMBDA(n,
LET(
sample, CONCAT(
bracketFromCode(bracketPair)(
RANDARRAY(1, n, -1, 1, TRUE)
)
),
APPENDCOLS(sample)(
bracketReport(bracketPair)(sample)
)
)
)
)
bracketFromCode
=LAMBDA(bracketPairString,
LAMBDA(c,
IF(0 <> c,
IF(0 < c,
MID(bracketPairString, 1, 1),
MID(bracketPairString, 2, 1)
),
"x"
)
)
)
codesFromBrackets
=LAMBDA(bracketPair,
LAMBDA(s,
LAMBDA(c,
LET(
posn, IFERROR(
FIND(c, bracketPair),
0
),
rem, "0 for non-bracket chars, (1, -1) for (open, close)",
IF(0 <> posn,
IF(1 < posn, -1, 1),
0
)
)
)(
MID(s,
SEQUENCE(1, LEN(s), 1, 1),
1
)
)
)
)
and also assuming the following generic bindings in the Name Manager for the WorkBook:
APPENDCOLS
=LAMBDA(xs,
LAMBDA(ys,
LET(
nx, COLUMNS(xs),
colIndexes, SEQUENCE(1, nx + COLUMNS(ys)),
rowIndexes, SEQUENCE(MAX(ROWS(xs), ROWS(ys))),
IFERROR(
IF(nx < colIndexes,
INDEX(ys, rowIndexes, colIndexes - nx),
INDEX(xs, rowIndexes, colIndexes)
),
NA()
)
)
)
)
CHARSROW
=LAMBDA(s,
MID(s,
SEQUENCE(1, LEN(s), 1, 1),
1
)
)
HEADCOL
=LAMBDA(xs,
LET(REM, "The first item of each column in xs",
INDEX(xs, 1, SEQUENCE(1, COLUMNS(xs)))
)
)
HEADROW
=LAMBDA(xs,
LET(REM, "The first item of each row in xs",
INDEX(
xs,
SEQUENCE(ROWS(xs)),
SEQUENCE(1, 1)
)
)
)
LASTCOL
=LAMBDA(xs,
INDEX(
xs,
SEQUENCE(ROWS(xs), 1, 1, 1),
COLUMNS(xs)
)
)
SCANLCOLS
=LAMBDA(op,
LAMBDA(a,
LAMBDA(xs,
APPENDCOLS(a)(
LET(
b, op(a, HEADROW(xs)),
IF(2 > COLUMNS(xs),
b,
SCANLCOLS(op)(b)(
TAILROW(xs)
)
)
)
)
)
)
)
TAILCOL
=LAMBDA(cols,
LET(REM, "The tail of each column in the grid.",
INDEX(
cols,
SEQUENCE(ROWS(cols) - 1, 1, 2, 1),
SEQUENCE(1, COLUMNS(cols))
)
)
)
TAILROW
=LAMBDA(xs,
LET(REM,"The tail of each row in the grid",
n, COLUMNS(xs) - 1,
IF(0 < n,
INDEX(
xs,
SEQUENCE(ROWS(xs), 1, 1, 1),
SEQUENCE(1, n, 2, 1)
),
NA()
)
)
)
- Output:
The formula in cell B2 defines the pair of values (random bracket sample, and verdict on balance), which populates the range B2:C2
| fx | =testRandomBrackets("[]")(10) | |||
|---|---|---|---|---|
| A | B | C | ||
| 1 | Random sample | Verdict | ||
| 2 | [[[[x[x]xx | Underclosed by end | ||
| 3 | [][]x[]]][ | Overclosed at char 8 | ||
| 4 | ][x[x]]x]x | Overclosed at char 1 | ||
| 5 | [x[]x[]]xx | OK | ||
| 6 | x]][[xxx[] | Overclosed at char 2 | ||
| 7 | [xxx[[[xxx | Underclosed by end | ||
| 8 | []x[[[xx]x | Underclosed by end | ||
| 9 | xxx[][xxx] | OK | ||
| 10 | ][x]x]]]][ | Overclosed at char 1 | ||
| 11 | ]xxxxx[x]] | Overclosed at char 1 | ||
Or applying the same bracketReport function to non-random samples, with a different bracket type:
| fx | =bracketReport("()")(C2) | |||
|---|---|---|---|---|
| A | B | C | ||
| 1 | Verdict | Sample | ||
| 2 | OK | (Non-random) sample string | ||
| 3 | OK | (Non-random) (sample) string | ||
| 4 | Overclosed at char 1 | )((Non-random) (sample) string) | ||
| 5 | Underclosed by end | ((Non-random) ((sample) string) | ||
| 6 | Overclosed at char 24 | ((Non-random)) (sample)) string) | ||
F#
let isBalanced str =
let rec loop count = function
| ']'::_ when count = 0 -> false
| '['::xs -> loop (count+1) xs
| ']'::xs -> loop (count-1) xs
| [] -> count = 0
| _::_ -> false
str |> Seq.toList |> loop 0
let shuffle arr =
let rnd = new System.Random()
Array.sortBy (fun _ -> rnd.Next()) arr
let generate n =
new string( String.replicate n "[]" |> Array.ofSeq |> shuffle )
for n in 1..10 do
let s = generate n
printfn "\"%s\" is balanced: %b" s (isBalanced s)
Output:
"[]" is balanced: true "][][" is balanced: false "][[]][" is balanced: false "[][[]][]" is balanced: true "[[]][[]][]" is balanced: true "[[]][[[]][]]" is balanced: true "][[[]][[[]][]]" is balanced: false "][[][][]][[]][[]" is balanced: false "][[]][][]][[]][[[]" is balanced: false "][[]]][[][]][[]][[[]" is balanced: false
Factor
USING: combinators formatting kernel math random sequences strings ;
IN: rosetta-code.balanced-brackets
: balanced? ( str -- ? )
0 swap [
{
{ CHAR: [ [ 1 + t ] }
{ CHAR: ] [ 1 - dup 0 >= ] }
[ drop t ]
} case
] all? swap zero? and ;
: bracket-pairs ( n -- str )
[ "[]" ] replicate "" concat-as ;
: balanced-brackets-main ( -- )
5 bracket-pairs randomize dup balanced? "" "not " ?
"String \"%s\" is %sbalanced.\n" printf ;
MAIN: balanced-brackets-main
The code below implements only the second part of the task: it reads from standard input an arbitrary string of opening and closing brackets, and checks whether it's balanced or not. Unlike the solution above, this one uses local variables.
USING: io formatting locals kernel math sequences unicode.case ;
IN: balanced-brackets
:: balanced ( str -- )
0 :> counter!
1 :> ok!
str
[ dup length 0 > ]
[ 1 cut swap
"[" = [ counter 1 + counter! ] [ counter 1 - counter! ] if
counter 0 < [ 0 ok! ] when
]
while
drop
ok 0 =
[ "NO" ]
[ counter 0 > [ "NO" ] [ "YES" ] if ]
if
print ;
readln
balanced
Fantom
class Main
{
static Bool matchingBrackets (Str[] brackets)
{
Int opened := 0
Int i := 0
while (i < brackets.size)
{
if (brackets[i] == "[")
opened += 1
else
opened -= 1
if (opened < 0) return false
i += 1
}
return true
}
public static Void main (Str[] args)
{
if (args.size == 1 && Int.fromStr(args[0], 10, false) != null)
{
n := Int.fromStr(args[0])
Str[] brackets := [,]
20.times
{
brackets = [,]
// create a random set of brackets
n.times { brackets.addAll (["[", "]"]) }
n.times { brackets.swap(Int.random(0..<2*n), Int.random(0..<2*n)) }
// report if matching or not
if (matchingBrackets(brackets))
echo (brackets.join(" ") + " Matching")
else
echo (brackets.join(" ") + " not matching")
}
}
}
}Output (for n=3):
[ ] [ ] [ ] Matching [ [ [ ] ] ] Matching ] [ [ ] ] [ not matching [ ] ] ] [ [ not matching ] ] [ ] [ [ not matching [ ] ] [ [ ] not matching [ ] ] [ [ ] not matching [ ] [ ] ] [ not matching [ [ ] ] [ ] Matching [ [ [ ] ] ] Matching [ ] ] [ [ ] not matching ] ] [ [ [ ] not matching [ ] ] [ [ ] not matching [ [ ] [ ] ] Matching [ ] [ ] [ ] Matching [ ] [ [ ] ] Matching [ [ [ ] ] ] Matching [ ] ] [ [ ] not matching ] ] [ ] [ [ not matching [ ] ] [ [ ] not matching
Forth
include lib/choose.4th ( n1 -- n2)
include lib/ctos.4th ( n -- a 1)
10 constant /[] \ maximum number of brackets
/[] string [] \ string with brackets
\ create string with brackets
: make[] ( --)
0 dup [] place /[] choose 0 ?do 2 choose 2* [char] [ + c>s [] +place loop
; \ empty string, fill with brackets
\ evaluate string
: eval[] ( --)
[] count 2dup over chars + >r swap type 0
begin \ setup string and count
over r@ < \ reached end of string?
while \ if not ..
dup 0< 0= \ unbalanced ]?
while \ if not ..
over c@ [char] \ - negate + swap char+ swap
repeat \ evaluate, goto next character
r> drop if ." NOT" then ." OK" cr drop
; \ evaluate string and print result
make[] eval[]
Examples:
[][[]] OK [[[[]][[ NOT OK ][[[]][] NOT OK ]][[[][ NOT OK []]]][][[ NOT OK []]][[]]] NOT OK OK [[[[]]]] OK [[]] OK [[[[]]]] OK [][[]] OK [] OK
Fortran
Please see the compilation and program execution result as comments at the top of this source:
! $ gfortran -g -O0 -std=f2008 -Wall f.f08 -o f.exe
! $ ./f
! compiles syntax error
! :
! : ][
! : ]][[
! :[[[]]]
! : ][[][]][
! : ][[]]][[[]
! : ]]]][]][[[[[
! : ]]]][][]][[[[[
! : ][[[]]]]][]][[[[
! : [[][]]][]]][[[][[]
! : ]]][[][[[[[[[[]]]]]]
! :[[][[[][]]][]]
! :[[[][]][][[[]][]][]]
program balanced_brackets
implicit none
integer :: N
character(len=20) :: brackets, fmt
write(6,*)'compiles syntax error'
call random_seed
do N=0, 10
call generate(N, brackets)
if (balanced(brackets)) then
fmt = '(a,a20)'
else
fmt = '(a,21x,a20)'
end if
write(6,fmt)':',brackets
end do
brackets = '[[][[[][]]][]]'
if (balanced(brackets)) then
fmt = '(a,a20)'
else
fmt = '(a,21x,a20)'
end if
write(6,fmt)':',brackets
N = 10
call generate(N, brackets)
do while (.not. balanced(brackets)) ! show a balanced set
call generate(N, brackets)
end do
fmt = '(a,a20)'
write(6,fmt)':',brackets
contains
logical function balanced(s)
implicit none
character(len=*), intent(in) :: s
integer :: i, a, n
n = len_trim(s)
a = 0
balanced = .true.
do i=1, n
if (s(i:i) == '[') then
a = a+1
else
a = a-1
end if
balanced = balanced .and. (0 <= a)
end do
end function balanced
subroutine generate(N, s)
implicit none
integer, intent(in) :: N
character(len=*), intent(out) :: s
integer :: L, R, i
real, dimension(2*N) :: harvest
character :: c
i = 1
L = 0
R = 0
s = ' '
call random_number(harvest)
do while ((L < N) .and. (R < N))
if (harvest(i) < 0.5) then
L = L+1
s(i:i) = '['
else
R = R+1
s(i:i) = ']'
end if
i = i+1
end do
c = merge('[', ']', L < N)
do while (i <= 2*N)
s(i:i) = c
i = i+1
end do
end subroutine generate
end program balanced_brackets
FreeBASIC
' FB 1.05.0 Win64
Function isBalanced(s As String) As Boolean
If s = "" Then Return True
Dim countLeft As Integer = 0 '' counts number of left brackets so far unmatched
Dim c As String
For i As Integer = 1 To Len(s)
c = Mid(s, i, 1)
If c = "[" Then
countLeft += 1
ElseIf countLeft > 0 Then
countLeft -= 1
Else
Return False
End If
Next
Return countLeft = 0
End Function
' checking examples in task description
Dim brackets(1 To 7) As String = {"", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"}
For i As Integer = 1 To 7
Print IIf(brackets(i) <> "", brackets(i), "(empty)"); Tab(10); IIf(isBalanced(brackets(i)), "OK", "NOT OK")
Next
' checking 7 random strings of brackets of length 8 say
Randomize
Dim r As Integer '' 0 will signify "[" and 1 will signify "]"
Dim s As String
For i As Integer = 1 To 7
s = Space(8)
For j As Integer = 1 To 8
r = Int(Rnd * 2)
If r = 0 Then
Mid(s, j) = "["
Else
Mid(s, j) = "]"
End If
Next j
Print s; Tab(10); IIf(isBalanced(s), "OK", "NOT OK")
Next i
Print
Print "Press any key to quit"
Sleep
Sample output (last 7 lines random) :
- Output:
(empty) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK ][]][[[[ NOT OK []][][]] NOT OK ][][[[]] NOT OK [[[[]]]] OK [][[[[][ NOT OK ][[[]][] NOT OK [][[[[][ NOT OK
FutureBasic
Filters out non-bracket characters prior to evaluation.
include "NSLog.incl"
local fn BracketBalance( strWithBracket as CFStringRef ) as CFStringRef
NSInteger i, bracketTracker = 0
CFStringRef result
CFCharacterSetRef bracketSet = fn CharacterSetWithCharactersInString( @"[]" )
CFCharacterSetRef bracketsOnlySet = fn CharacterSetInvertedSet( bracketSet )
CFArrayRef trimmedSArray = fn StringComponentsSeparatedByCharactersInSet( strWithBracket, bracketsOnlySet )
CFStringRef trimmedStr = fn ArrayComponentsJoinedByString( trimmedSArray, @"" )
NSUInteger strLen = len( trimmedStr )
// Empty string, no brackets
if ( strLen == 0 ) then result = @"No brackets" : exit fn
// String with odd number of brackets is unbalanced
if ( strLen mod 2 ) then result = @"Unbalanced" : exit fn
for i = 0 to strLen - 1
CFStringRef bracket = fn StringWithFormat( @"%C", fn StringCharacterAtIndex( trimmedStr, i ) )
if fn StringisEqual( bracket, @"[" ) then bracketTracker++
if fn StringisEqual( bracket, @"]" ) then bracketTracker--
if bracketTracker < 0 then result = @"Unbalanced" : break
next
if bracketTracker == 0 then result = @"Balanced"
end fn = result
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"" ) ), @"" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[" ) ), @"[" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"]" ) ), @"]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[]" ) ), @"[]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[[]" ) ), @"[[]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[]]" ) ), @"[]]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[][]" ) ), @"[][]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"][" ) ), @"][" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"][][" ) ), @"][][" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[[]][][][[][]]" ) ), @"[[]][][][[][]]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"][[]][][][]]][[" ) ), @"][[]][][][]]][[" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[[[abc]][[d]]]]]" ) ), @"[[[abc]][[def]]]]]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[[[abc]]][[[[[d]]]]]" ) ), @"[[[abc]]][[[[[def]]]]]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"[][abc]]][[[[[d]]]]]" ) ), @"[][abc]]][[[[[def]]]]]" )
NSLog( @"%12s: %@", fn StringUTF8String( fn BracketBalance( @"The quick brown fox" ) ), @"The quick brown fox" )
HandleEvents- Output:
No brackets:
Unbalanced: [
Unbalanced: ]
Balanced: []
Unbalanced: [[]
Unbalanced: []]
Balanced: [][]
Unbalanced: ][
Unbalanced: ][][
Balanced: [[]][][][[][]]
Unbalanced: ][[]][][][]]][[
Unbalanced: [[[abc]][[def]]]]]
Balanced: [[[abc]]][[[[[def]]]]]
Unbalanced: [][abc]]][[[[[def]]]]]
No brackets: The quick brown fox
Gambas
Click this link to run this code
'Altered to prevent lines starting with ']' or ending with '[' being generated as they can't work
siNumberOfBrackets As Short = 20 'Maximum amount of brackets in a line
siNumberOfLines As Short = 20 'Amount of lines to test
'----
Public Sub Main()
Dim sBrks As String[] = GenerateBrackets() 'Get random array to check
Dim sTemp, sHold, sWork As String 'Working variables
Dim siCount As Short 'Counter
For Each sTemp In sBrks 'For each line in the sBrk array (e.g. '[][][][[[[]][]]]')
sWork = sTemp 'Make sWork = sTemp
Repeat 'Repeat
sHold = sWork 'Make sHold = sWork
sWork = Replace(sWork, "[]", "") 'Remove all brackets that match '[]'
Until sHold = sWork 'If sHold = sWork then there are no more '[]' matches
If sWork = "" Then 'So if all the brackets 'Nested' correctly sWork will be empty
Print " OK "; 'Print 'OK'
Else 'Else they did not all match
Print "NOT OK "; 'So print 'NOT OK'
Endif
For siCount = 1 To Len(sTemp) 'Loop through the line of brackets
Print Mid(sTemp, siCount, 1) & " "; 'Print each bracket + a space to make it easier to read
Next
Print 'Print a new line
Next
End
'----
Public Sub GenerateBrackets() As String[] 'Generates an array of random quantities of '[' and ']'
Dim siQty As New Short[] 'To store the random number (of brackets) to put in a line
Dim sBrk As New String[] 'To store the lines of brackets
Dim siNum, siEnd, siLoop As Short 'Various counters
Dim sTemp As String 'Temp string
Repeat 'Repeat
siNum = Rand(0, siNumberOfBrackets) 'Pick a number between 0 and the total number of brackets requested
If Even(siNum) Then siQty.Add(siNum) 'If the number is even then add the number to siQty
Until siQty.Count = siNumberOfLines 'Keep going until we have the number of lines requested
For Each siNum In siQty 'For each number in siQty..(e.g. 6)
Do
siEnd = Rand(0, 1) 'Generate a 0 or a 1
If siEnd = 0 Then sTemp &= "[" 'If '0' then add a '[' bracket
If siEnd = 1 Then sTemp &= "]" 'If '1' then add a ']' bracket
If siNum = 0 Then 'If siNum = 0 then..
sBrk.Add("") 'Add '0' to the array
sTemp = "" 'Clear sTemp
Break 'Exit the Do Loop
Endif
If Len(sTemp) = siNum Then 'If the length of sTemp = the required amount then..
If sTemp Not Begins "]" And sTemp Not Ends "[" Then 'Check to see that sTemp does not start with "]" and does not end with a "["
sBrk.Add(sTemp) 'Add it to the array
sTemp = "" 'Clear sTemp
Break 'Exit the Do Loop
Else 'Else
sTemp = "" 'Clear sTemp
End If 'Try again!
Endif
Loop
Next
Return sBrk 'Return the sBrk array
End
Output:
NOT OK [ ] ] [ [ ] [ [ ] [ [ [ ] [ [ ] [ ]
NOT OK [ [ [ ] [ [ ] [ [ ] ] [ ] ]
NOT OK [ ] [ [ [ ] ] [ [ ] ] ] [ ] ] [ ] ] ] ]
NOT OK [ [ [ ] [ ] ] ] ] ] [ [ ] ] [ ] [ [ ] ]
NOT OK [ [ ] ] ] ]
NOT OK [ ] ] [ [ ] [ ] [ ]
NOT OK [ [ [ ] [ ]
OK [ ]
NOT OK [ ] ] ] [ ]
NOT OK [ [ ] ] ] ]
OK [ [ [ [ ] ] [ ] [ ] ] ]
OK [ ]
OK [ ] [ ]
NOT OK [ ] ] ] [ ] [ [ [ [ ] [ [ ] [ ]
NOT OK [ ] ] ] [ [ ] ] ] [ ] ] ] ]
NOT OK [ ] ] ] ] ] [ [ ] [ ] ] ] [ ] [ [ [ [ ]
GAP
Balanced := function(L)
local c, r;
r := 0;
for c in L do
if c = ']' then
r := r - 1;
if r < 0 then
return false;
fi;
elif c = '[' then
r := r + 1;
fi;
od;
return r = 0;
end;
Balanced("");
# true
Balanced("[");
# false
Balanced("]");
# false
Balanced("[]");
# true
Balanced("][");
# false
Balanced("[[][]]");
# true
Balanced("[[[]][]]]");
# false
GDScript
extends MainLoop
func generate_brackets(n: int) -> String:
var brackets: Array[String] = []
# Add opening and closing brackets
brackets.resize(2*n)
for i in range(0, 2*n, 2):
brackets[i] = "["
brackets[i+1] = "]"
brackets.shuffle()
return "".join(brackets)
func is_balanced(str: String) -> bool:
var unclosed_brackets := 0
for c in str:
match c:
"[":
unclosed_brackets += 1
"]":
if unclosed_brackets == 0:
return false
unclosed_brackets -= 1
_:
return false
return unclosed_brackets == 0
func _process(_delta: float) -> bool:
randomize()
for i in range(6):
var bracket_string := generate_brackets(i)
if is_balanced(bracket_string):
print("%sOK" % bracket_string.rpad(13))
else:
print("%sNOT OK" % bracket_string.rpad(11))
return true # Exit
Go
package main
import (
"bytes"
"fmt"
"math/rand"
"time"
)
func init() {
rand.Seed(time.Now().UnixNano())
}
func generate(n uint) string {
a := bytes.Repeat([]byte("[]"), int(n))
for i := len(a) - 1; i >= 1; i-- {
j := rand.Intn(i + 1)
a[i], a[j] = a[j], a[i]
}
return string(a)
}
func testBalanced(s string) {
fmt.Print(s + ": ")
open := 0
for _,c := range s {
switch c {
case '[':
open++
case ']':
if open == 0 {
fmt.Println("not ok")
return
}
open--
default:
fmt.Println("not ok")
return
}
}
if open == 0 {
fmt.Println("ok")
} else {
fmt.Println("not ok")
}
}
func main() {
rand.Seed(time.Now().UnixNano())
for i := uint(0); i < 10; i++ {
testBalanced(generate(i))
}
testBalanced("()")
}
Output:
: ok ][: not ok ]][[: not ok [[][]]: ok [][[][]]: ok [[[][][]]]: ok ]][[]]][[[[]: not ok ]][[[]][[][[]]: not ok [[[[[]]][]]][]][: not ok [][[][[]][][[][]]]: ok (): not ok
Groovy
Generate Arbitrary String of Bracket Pairs:
def random = new Random()
def factorial = { (it > 1) ? (2..it).inject(1) { i, j -> i*j } : 1 }
def makePermutation;
makePermutation = { string, i ->
def n = string.size()
if (n < 2) return string
def fact = factorial(n-1)
assert i < fact*n
def index = i.intdiv(fact)
string[index] + makePermutation(string[0..<index] + string[(index+1)..<n], i % fact)
}
def randomBrackets = { n ->
if (n == 0) return ''
def base = '['*n + ']'*n
def p = random.nextInt(factorial(n*2))
makePermutation(base, p)
}
Check Balance of Bracket String:
boolean balancedBrackets(String brackets, int depth=0) {
if (brackets == null || brackets.empty) return depth == 0
switch (brackets[0]) {
case '[':
return brackets.size() > 1 && balancedBrackets(brackets[1..-1], depth + 1)
case ']':
return depth > 0 && (brackets.size() == 1 || balancedBrackets(brackets[1..-1], depth - 1))
default:
return brackets.size() == 1 ? depth == 0 : balancedBrackets(brackets[1..-1], depth)
}
}
Test:
Set brackets = []
(0..100).each {
(0..8).each { r ->
brackets << randomBrackets(r)
}
}
brackets.sort { a, b ->
a.size() <=> b.size() ?: a <=> b
} .each {
def bal = balancedBrackets(it) ? "balanced: " : "unbalanced: "
println "${bal} ${it}"
}
Output:
balanced: balanced: [] unbalanced: ][ balanced: [[]] balanced: [][] unbalanced: []][ unbalanced: ][[] unbalanced: ][][ unbalanced: ]][[ balanced: [[[]]] balanced: [[][]] balanced: [[]][] unbalanced: [[]]][ balanced: [][[]] balanced: [][][] unbalanced: [][]][ unbalanced: []][[] unbalanced: []][][ unbalanced: []]][[ unbalanced: ][[[]] unbalanced: ][[][] unbalanced: ][[]][ unbalanced: ][][[] unbalanced: ][][][ unbalanced: ][]][[ unbalanced: ]][[[] unbalanced: ]][[][ unbalanced: ]][][[ unbalanced: ]]][[[ balanced: [[[[]]]] balanced: [[[][]]] balanced: [[[]][]] balanced: [[[]]][] unbalanced: [[[]]]][ balanced: [[][[]]] balanced: [[][]][] unbalanced: [[][]]][ balanced: [[]][[]] balanced: [[]][][] unbalanced: [[]][]][ unbalanced: [[]]][[] unbalanced: [[]]]][[ balanced: [][[][]] balanced: [][[]][] unbalanced: [][]][[] unbalanced: [][]][][ unbalanced: [][]]][[ unbalanced: []][[][] unbalanced: []][[]][ unbalanced: []][][[] unbalanced: []][][][ unbalanced: []][]][[ unbalanced: []]][[[] unbalanced: []]][[][ unbalanced: []]]][[[ unbalanced: ][[[[]]] unbalanced: ][[[]][] unbalanced: ][[[]]][ unbalanced: ][[][][] unbalanced: ][[][]][ unbalanced: ][][[[]] unbalanced: ][][[][] unbalanced: ][][[]][ unbalanced: ][][][[] unbalanced: ][][][][ unbalanced: ][][]][[ unbalanced: ][]][[[] unbalanced: ][]][[][ ... <SOME OF THE SAME CUT> balanced: [[]][[][][[]]] unbalanced: [[]][[][]][]][ balanced: [[]][[]][][[]] balanced: [[]][][[][[]]] balanced: [[]][][][[][]] unbalanced: [[]][][][]]][[ unbalanced: [[]][][]][[]][ unbalanced: [[]][]][[[][]] unbalanced: [[]][]][[][[]] unbalanced: [[]][]][[][][] unbalanced: [[]][]][][[][] unbalanced: [[]][]][][]][[ unbalanced: [[]][]]][[][][ unbalanced: [[]][]]][][[][ unbalanced: [[]]][[[]][][] unbalanced: [[]]][[][[][]] unbalanced: [[]]][[][[]]][ unbalanced: [[]]][][[[[]]] unbalanced: [[]]][][[]]][[ unbalanced: [[]]][][]][[[] unbalanced: [[]]][]][[[]][ unbalanced: [[]]][]][[][][ unbalanced: [[]]]][[][[]][ unbalanced: [[]]]][][[[]][ unbalanced: [[]]]][][[][[] unbalanced: [[]]]][][]][[[ unbalanced: [[]]]]][[[[]][ unbalanced: [[]]]]][][[[[] unbalanced: [[]]]]]][][[[[ unbalanced: [[]]]]]]][[[[[ balanced: [[[[[[[]]]]][]]] unbalanced: [[[[[[[]]]]]]]][ balanced: [[[[[[][]]]][]]] unbalanced: [[[[[[][]]]]]]][ balanced: [[[[[[]]][][]]]] balanced: [[[[[[]]]][[]]]] balanced: [[[[[[]]]][]][]] balanced: [[[[[[]]]][]]][] balanced: [[[[[[]]]]][][]] unbalanced: [[[[[[]]]]][]]][ balanced: [[[[[[]]]]]][][] unbalanced: [[[[[[]]]]]][]][ balanced: [[[[[][][[]]]]]] balanced: [[[[[][][]][]]]] balanced: [[[[[][]][[]]]]] balanced: [[[[[][]][]][]]] balanced: [[[[[][]]]]][][] unbalanced: [[[[[][]]]]]]][[ balanced: [[[[[]][[][]]]]] balanced: [[[[[]][[]]]]][] balanced: [[[[[]][][[]]]]] balanced: [[[[[]][]][[]]]] balanced: [[[[[]][]]]][[]] balanced: [[[[[]]][[[]]]]] balanced: [[[[[]]][[][]]]] unbalanced: [[[[[]]][[]]]]][ balanced: [[[[[]]][][][]]] balanced: [[[[[]]][]][[]]] balanced: [[[[[]]][]][]][] unbalanced: [[[[[]]][]][]]][ balanced: [[[[[]]][]]][[]] unbalanced: [[[[[]]]][]][]][ balanced: [[[[[]]]]][[]][] balanced: [[[[[]]]]][][[]] balanced: [[[[[]]]]][][][] unbalanced: [[[[[]]]]][]][[] unbalanced: [[[[[]]]]]][[]][ unbalanced: [[[[[]]]]]][][[] balanced: [[[[][[[[]]]]]]] balanced: [[[[][[[][]]]]]] balanced: [[[[][[]][[]]]]] balanced: [[[[][[]][][]]]] balanced: [[[[][[]]]]][][] balanced: [[[[][][][][]]]] balanced: [[[[][][][]]][]] balanced: [[[[][][]][][]]] balanced: [[[[][][]]][][]] unbalanced: [[[[][][]]][]]][ balanced: [[[[][][]]]][][] balanced: [[[[][]][[[]]]]] balanced: [[[[][]][[]]]][] balanced: [[[[][]][][]][]] unbalanced: [[[[][]]][]]]][[ balanced: [[[[][]]]][[[]]] balanced: [[[[][]]]][][[]] unbalanced: [[[[][]]]]][][][ unbalanced: [[[[][]]]]]]][[[ balanced: [[[[]][[][]][]]] balanced: [[[[]][[]]]][[]] balanced: [[[[]][][[][]]]] unbalanced: [[[[]][][[]]]]][ balanced: [[[[]][][][]][]] balanced: [[[[]][][]][[]]] balanced: [[[[]][][]][][]] balanced: [[[[]][][]][]][] balanced: [[[[]][][]]][[]] unbalanced: [[[[]][]][]][]][ balanced: [[[[]][]]][[]][] unbalanced: [[[[]][]]]][[][] unbalanced: [[[[]][]]]][[]][ unbalanced: [[[[]][]]]]][[[] balanced: [[[[]]][[]]][[]] balanced: [[[[]]][[]]][][] balanced: [[[[]]][][][[]]] balanced: [[[[]]][]][[]][] unbalanced: [[[[]]][]][[]]][ unbalanced: [[[[]]][]]][[]][ unbalanced: [[[[]]][]]][]][[ unbalanced: [[[[]]][]]]][[[] balanced: [[[[]]]][[[[]]]] balanced: [[[[]]]][[[][]]] balanced: [[[[]]]][[]][][] unbalanced: [[[[]]]][[]][]][ unbalanced: [[[[]]]][][]]][[ unbalanced: [[[[]]]][]][[[]] unbalanced: [[[[]]]][]][[]][ unbalanced: [[[[]]]][]]][][[ unbalanced: [[[[]]]][]]]][[[ unbalanced: [[[[]]]]][][][[] unbalanced: [[[[]]]]][][]][[ unbalanced: [[[[]]]]]][[]][[ unbalanced: [[[[]]]]]][][][[
Haskell
The simplest solution exploits the idea of stack-based automaton, which could be implemented by a fold.
isMatching :: String -> Bool
isMatching = null . foldl aut []
where
aut ('[':s) ']' = s
-- aut ('{':s) '}' = s -- automaton could be extended
aut s x = x:s
This generates an infinite stream of correct balanced brackets expressions:
brackets = filter isMatching
$ [1.. ] >>= (`replicateM` "[]{}")
λ> take 10 brackets
["[]","{}","[[]]","[][]","[]{}","[{}]","{[]}","{{}}","{}[]","{}{}"]
In case the index of unmatched opening bracket is need to be found, following solution is suitable.
import Control.Monad
import System.Random
import Text.Printf
import VShuffle
-- Return whether a string contains balanced brackets. Nothing indicates a
-- balanced string, while (Just i) means an imbalance was found at, or just
-- after, the i'th bracket. We assume the string contains only brackets.
isBalanced :: String -> Maybe Int
isBalanced = bal (-1) 0
where
bal :: Int -> Int -> String -> Maybe Int
bal _ 0 [] = Nothing
bal i _ [] = Just i
bal i (-1) _ = Just i
bal i n ('[':bs) = bal (i + 1) (n + 1) bs
bal i n (']':bs) = bal (i + 1) (n - 1) bs
-- Print a string, indicating whether it contains balanced brackets. If not,
-- indicate the bracket at which the imbalance was found.
check :: String -> IO ()
check s = maybe (good s) (bad s) (isBalanced s)
where
good = printf "Good \"%s\"\n"
bad s n = printf "Bad \"%s\"\n%*s^\n" s (n + 6) " "
main :: IO ()
main = do
let bs = cycle "[]"
rs <- replicateM 10 newStdGen
zipWithM_ (\n r -> check $ shuffle (take n bs) r) [0,2 ..] rs
We put our list shuffling function in a separate module. For efficiency we use mutable vectors, although for the short lists in our example it doesn't really matter.
module VShuffle
( shuffle
) where
import Data.List (mapAccumL)
import System.Random
import Control.Monad.ST
import qualified Data.Vector as V
import qualified Data.Vector.Generic.Mutable as M
-- Generate a list of array index pairs, each corresponding to a swap.
pairs
:: (Enum a, Random a, RandomGen g)
=> a -> a -> g -> [(a, a)]
pairs l u r = snd $ mapAccumL step r [l .. pred u]
where
step r i =
let (j, r') = randomR (i, u) r
in (r', (i, j))
-- Return a random permutation of the list. We use the algorithm described in
-- http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#The_modern_algorithm.
shuffle
:: (RandomGen g)
=> [a] -> g -> [a]
shuffle xs r =
V.toList . runST $
do v <- V.unsafeThaw $ V.fromList xs
mapM_ (uncurry $ M.swap v) $ pairs 0 (M.length v - 1) r
V.unsafeFreeze v
Here's some sample output.
Good ""
Bad "]["
^
Good "[[]]"
Bad "[]][]["
^
Bad "[]]][][["
^
Bad "][][[[]][]"
^
Bad "[[][][]]][]["
^
Bad "][]][[[][][[]]"
^
Good "[[][[][[]]][[]]]"
Bad "]]][[[][][][[][]]["
^
and scanl also yields a simple fit when we want the index of the tipping point:
import Control.Applicative ((<|>))
import Data.List (findIndex, replicate, scanl)
import Data.List.Split (chunksOf)
import System.Random
-------------------- BALANCED BRACKETS -------------------
nesting :: String -> [Int]
nesting = tail . scanl (flip level) 0
where
level '[' = succ
level ']' = pred
level _ = id
bracketProblemIndex :: String -> Maybe Int
bracketProblemIndex s =
findIndex (< 0) depths <|> unClosed
where
depths = nesting s
unClosed
| 0 /= last depths = Just $ pred (length s)
| otherwise = Nothing
--------------------------- TEST -------------------------
main :: IO ()
main = do
let g = mkStdGen 137
mapM_ (putStrLn . showProblem) $
chunksOf
6
(bracket <$> take 60 (randomRs (0, 1) g))
showProblem s =
case bracketProblemIndex s of
Just i -> s <> ": Unmatched\n" <> replicate i ' ' <> "^"
_ -> s <> ": OK\n"
bracket :: Int -> Char
bracket 0 = '['
bracket _ = ']'
- Output:
]][]][: Unmatched
^
][[][[: Unmatched
^
][][[[: Unmatched
^
]][][]: Unmatched
^
[[][]]: OK
]]][]]: Unmatched
^
[][][[: Unmatched
^
[]]]]]: Unmatched
^
][[][[: Unmatched
^
[][]][: Unmatched
^
Icon and Unicon
Output:
> isbal.exe 2 3 3 3 3 3 3 3 4 4 4 "[[]]" is balanced. "]]]]]]" is unbalanced "]]]]]]" is unbalanced "[][][]" is balanced. "]][[[]" is unbalanced "[[[][[" is unbalanced "]]]]]]" is unbalanced "[]]]]]" is unbalanced "]][]][]]" is unbalanced "[[[[[][[" is unbalanced "[[[[[][]" is unbalanced
J
Solution:
bracketDepth =: '[]' -&(+/\)/@:(=/) ]
checkBalanced =: _1 -.@e. bracketDepth
genBracketPairs =: (?~@# { ])@#"0 1&'[]' NB. bracket pairs in arbitrary order
Examples:
(, ' ' , ('bad';'OK') {::~ checkBalanced)"1 genBracketPairs i. 10
OK
][ bad
][[] bad
[[[]]] OK
[][[]][] OK
[][[[][]]] OK
[]][]][]][[[ bad
[[]][[][][]][] OK
]]]][[][][[[[]][ bad
[]]][][][[[[]][[]] bad
Comments: This task highlights the versatility and usefulness of J's scanning modifiers, / and \.
The checkBalanced verb would need modification ( checkBalanced =: ((0 = {:) *. _1 -.@e. ])@bracketDepth ) if the task were extended to include uneven numbers of opening and closing brackets.
Java
public class BalancedBrackets {
public static boolean hasBalancedBrackets(String str) {
int brackets = 0;
for (char ch : str.toCharArray()) {
if (ch == '[') {
brackets++;
} else if (ch == ']') {
brackets--;
} else {
return false; // non-bracket chars
}
if (brackets < 0) { // closing bracket before opening bracket
return false;
}
}
return brackets == 0;
}
public static String generateBalancedBrackets(int n) {
assert n % 2 == 0; // if n is odd we can't match brackets
char[] ans = new char[n];
int openBracketsLeft = n / 2;
int unclosed = 0;
for (int i = 0; i < n; i++) {
if (Math.random() >= 0.5 && openBracketsLeft > 0 || unclosed == 0) {
ans[i] = '[';
openBracketsLeft--;
unclosed++;
} else {
ans[i] = ']';
unclosed--;
}
}
return String.valueOf(ans);
}
public static void main(String[] args) {
for (int i = 0; i <= 16; i += 2) {
String brackets = generateBalancedBrackets(i);
System.out.println(brackets + ": " + hasBalancedBrackets(brackets));
}
String[] tests = {"", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"};
for (String test : tests) {
System.out.println(test + ": " + hasBalancedBrackets(test));
}
}
}
Sample output (generate uses random numbers, so it should not be the same every time):
: true []: true [[]]: true [[]][]: true [][][][]: true [][[][[]]]: true [[][[][][]]]: true [[][][]][[[]]]: true [][[[][[][[]]]]]: true : true []: true ][: false [][]: true ][][: false [[][]]: true []][[]: false
Extended
import java.util.ArrayDeque;
import java.util.Deque;
public class BalancedBrackets {
public static boolean areSquareBracketsBalanced(String expr) {
return isBalanced(expr, "", "", "[", "]", false);
}
public static boolean areBracketsBalanced(String expr) {
return isBalanced(expr, "", "", "{([", "})]", false);
}
public static boolean areStringAndBracketsBalanced(String expr) {
return isBalanced(expr, "'\"", "\\\\", "{([", "})]", true);
}
public static boolean isBalanced(String expr, String lit, String esc, String obr, String cbr, boolean other) {
boolean[] inLit = new boolean[lit.length()];
Deque<Character> stack = new ArrayDeque<Character>();
for (int i=0; i<expr.length(); i+=1) {
char c = get(expr, i);
int x;
if ((x = indexOf(inLit, true)) != -1) {
if (c == get(lit, x) && get(expr, i-1) != get(esc, x)) inLit[x] = false;
}
else if ((x = indexOf(lit, c)) != -1)
inLit[x] = true;
else if ((x = indexOf(obr, c)) != -1)
stack.push(get(cbr, x));
else if (indexOf(cbr, c) != -1) {
if (stack.isEmpty() || stack.pop() != c) return false;
}
else if (!other)
return false;
}
return stack.isEmpty();
}
static int indexOf(boolean[] a, boolean b) {
for (int i=0; i<a.length; i+=1) if (a[i] == b) return i;
return -1;
}
static int indexOf(String s, char c) {
return s.indexOf(c);
}
static char get(String s, int i) {
return s.charAt(i);
}
public static void main(String[] args) {
System.out.println("With areSquareBracketsBalanced:");
for (String s: new String[] {
"", "[]", "[][]", "[[][]]", "][", "][][", "[]][[]", "[", "]"
}
) {
System.out.printf("%s: %s\n", s, areSquareBracketsBalanced(s));
}
System.out.println("\nBut also with areStringAndBracketsBalanced:");
for (String s: new String[] {
"x[]", "[x]", "[]x", "([{}])", "([{}]()", "([{ '([{\\'([{' \"([{\\\"([{\" }])",
}
) {
System.out.printf("%s: %s\n", s, areStringAndBracketsBalanced(s));
}
}
}
- Output:
With areSquareBracketsBalanced:
: true
[]: true
[][]: true
[[][]]: true
][: false
][][: false
[]][[]: false
[: false
]: false
But also with areStringAndBracketsBalanced:
x[]: true
[x]: true
[]x: true
([{}]): true
([{}](): false
([{ '([{\'([{' "([{\"([{" }]): true
JavaScript
ES5
Iterative
function shuffle(str) {
var a = str.split(''), b, c = a.length, d
while (c) b = Math.random() * c-- | 0, d = a[c], a[c] = a[b], a[b] = d
return a.join('')
}
function isBalanced(str) {
var a = str, b
do { b = a, a = a.replace(/\[\]/g, '') } while (a != b)
return !a
}
var M = 20
while (M-- > 0) {
var N = Math.random() * 10 | 0, bs = shuffle('['.repeat(N) + ']'.repeat(N))
console.log('"' + bs + '" is ' + (isBalanced(bs) ? '' : 'un') + 'balanced')
}
Sample output:
"[]" is balanced "]][[]][[[]" is unbalanced "]][[[][][][]][" is unbalanced "[][[[[][][[[]]]]]]" is balanced "][" is unbalanced "[[[]]]][[]" is unbalanced "][[]" is unbalanced "][[][]][[[]]" is unbalanced "[[][]]][" is unbalanced "[[[]]][[]]]][][[" is unbalanced "[]][[]]][[[[][]]" is unbalanced "[]" is balanced "][]][[][" is unbalanced "[[]][[][]]" is balanced "[[]]" is balanced "]][]][[]][[[" is unbalanced "][]][][[" is unbalanced "[[]]" is balanced "][][" is unbalanced "[[]]][][][[]][" is unbalanced
Another solution
console.log("Supplied examples");
var tests = ["", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"];
for (var test of tests)
{
console.log("The string '" + test + "' is " +
(isStringBalanced(test) ? "" : "not ") + "OK.");
}
console.log();
console.log("Random generated examples");
for (var example = 1; example <= 10; example++)
{
var test = generate(Math.floor(Math.random() * 10) + 1);
console.log("The string '" + test + "' is " +
(isStringBalanced(test) ? "" : "not ") + "OK.");
}
function isStringBalanced(str)
{
var paired = 0;
for (var i = 0; i < str.length && paired >= 0; i++)
{
var c = str[i];
if (c == '[')
paired++;
else if (c == ']')
paired--;
}
return (paired == 0);
}
function generate(n)
{
var opensCount = 0, closesCount = 0;
// Choose at random until n of one type generated
var generated = "";
while (opensCount < n && closesCount < n)
{
switch (Math.floor(Math.random() * 2) + 1)
{
case 1:
opensCount++;
generated += "[";
break;
case 2:
closesCount++;
generated += "]";
break;
default:
break;
}
}
// Now pad with the remaining other brackets
generated +=
opensCount == n ? "]".repeat(n - closesCount) : "[".repeat(n - opensCount);
return generated;
}
- Output:
Supplied examples The string '' is OK. The string '[]' is OK. The string '][' is not OK. The string '[][]' is OK. The string '][][' is not OK. The string '[[][]]' is OK. The string '[]][[]' is not OK. Random generated examples The string ']]][[[[[]][[[]]]]][[' is not OK. The string '[][]]][]][[]]][[[[' is not OK. The string ']][][[[][][][]' is not OK. The string '][]][[][[[][]]][' is not OK. The string '[]][[[][]]' is not OK. The string ']]][[[[]]]][]]][[[[[' is not OK. The string ']]]][][]][[[[[' is not OK. The string '[][[[[][]][]]]' is OK. The string '][[]]][[[[]]][[[]]' is not OK. The string '[]' is OK.
ES6
Functional
With visual indication of where the balance fails:
(() => {
'use strict';
// ---------------- BALANCED BRACKETS ----------------
// firstUnbalancedBracket :: String -> String -> Maybe Int
const firstUnbalancedBracket = brackets =>
haystack => {
const [openBracket, closeBracket] = [...brackets];
const go = (xs, iDepth, iCharPosn) =>
// iDepth: initial nesting depth (0 = closed)
// iCharPosn: starting character position
0 < xs.length ? (() => {
const
h = xs[0],
tail = xs.slice(1),
iNext = iDepth + (
brackets.includes(h) ? (
openBracket === h ? (
1
) : -1
) : 0
);
return 0 > iNext ? (
Just(iCharPosn) // Unmatched closing bracket.
) : 0 < tail.length ? go(
tail, iNext, 1 + iCharPosn
) : 0 !== iNext ? (
Just(iCharPosn)
) : Nothing();
})() : 0 !== iDepth ? (
Just(iCharPosn)
) : Nothing();
return go([...haystack], 0, 0);
};
// ---------------------- TEST -----------------------
// main :: IO ()
const main = () => {
const
intPairs = 6,
strPad = ' '.repeat(4 + (2 * intPairs));
console.log(
enumFromTo(0)(intPairs)
.map(pairCount => {
const
stringLength = 2 * pairCount,
strSample = randomBrackets(stringLength);
return "'" + strSample + "'" +
strPad.slice(2 + stringLength) + maybe('OK')(
iUnMatched => 'problem\n' +
' '.repeat(1 + iUnMatched) + '^'
)(
firstUnbalancedBracket('[]')(strSample)
);
}).join('\n')
);
};
// Int -> String
const randomBrackets = n =>
enumFromTo(1)(n)
.map(() => Math.random() < 0.5 ? (
'['
) : ']').join('');
// --------------------- GENERIC ---------------------
// Just :: a -> Maybe a
const Just = x => ({
type: 'Maybe',
Nothing: false,
Just: x
});
// Nothing :: Maybe a
const Nothing = () => ({
type: 'Maybe',
Nothing: true,
});
// enumFromTo :: Int -> Int -> [Int]
const enumFromTo = m =>
n => !isNaN(m) ? (
Array.from({
length: 1 + n - m
}, (_, i) => m + i)
) : enumFromTo_(m)(n);
// maybe :: b -> (a -> b) -> Maybe a -> b
const maybe = v =>
// Default value (v) if m is Nothing, or f(m.Just)
f => m => m.Nothing ? (
v
) : f(m.Just);
// ---
return main();
})();
- Output:
'' OK
'[]' OK
'[][[' problem
^
'[]]][[' problem
^
'[][[][[[' problem
^
'[][[[]][]]' OK
']]][[][][][]' problem
^
jq
Works with gojq, the Go implementation of jq.
In this entry, two solutions are given: the first uses an external source of entropy and jq's `until` control structure; the second uses a low-entropy PRNG based on jq's `now`, and `gsub/2.`
High entropy solution using `until`
< /dev/random tr -cd '0-9' | fold -w 1 | jq -Mcnr '
# Output: a PRN in range(0;$n) where $n is .
def prn:
if . == 1 then 0
else . as $n
| (($n-1)|tostring|length) as $w
| [limit($w; inputs)] | join("") | tonumber
| if . < $n then . else ($n | prn) end
end;
def prb: 2 | prn == 0;
def balanced:
{array: explode, parity: 0}
| until( .result | type == "boolean";
if .array == [] then .result = (.parity == 0)
else .parity += (.array[0] | if . == 91 then 1 else -1 end)
| if .parity < 0 then .result = false
else .array |= .[1:]
end
end ).result ;
def task($n):
if $n%2 == 1 then null
else [ (range(0; $n) | if prb then "[" else "]" end) // ""]
| add
| "\(.): \(balanced)"
end;
task(0),
task(2),
(range(0;10) | task(4))
- Output:
: true [[: false [][[: false ][[[: false ]][[: false [[]]: true ]][[: false ][[[: false [[[[: false [][[: false ][[[: false []][: false
Low entropy solution with `gsub`
def prb: (now|tostring[-1:] | tonumber) % 2 == 0;
def balanced:
if length==0 then true
elif .[:1] == "]" then false
else test("[[][]]") and (gsub("[[][]]"; "") | balanced)
end;
def task($n):
if $n%2 == 1 then null
else
(reduce range(0; $n) as $i ("";
. + (if prb then "[" else "]" end) ))
| "\(.): \(balanced)"
end;
task(0),
task(2),
(range(0;10) | task(4))- Output:
Similar to above.
Julia
using Printf
function balancedbrackets(str::AbstractString)
i = 0
for c in str
if c == '[' i += 1 elseif c == ']' i -=1 end
if i < 0 return false end
end
return i == 0
end
brackets(n::Integer) = join(shuffle(collect(Char, "[]" ^ n)))
for (test, pass) in map(x -> (x, balancedbrackets(x)), collect(brackets(i) for i = 0:8))
@printf("%22s%10s\n", test, pass ? "pass" : "fail")
end
- Output:
pass
][ fail
[][] pass
][[]][ fail
[[[]]][] pass
]]]][[[][[ fail
]]][[][][[[] fail
]][]][][[[][][ fail
[]][]]]][[[][[[] fail
One-line version:
balancedbrackets(str::AbstractString) = foldl((x, y) -> x < 0 ? -1 : x + y, collect((x == '[') - (x == ']') for x in str), init = 0) == 0
K
gen_brackets:{"[]"@x _draw 2}
check:{r:(-1;1)@"["=x; *(0=+/cs<'0)&(0=-1#cs:+\r)}
{(x;check x)}' gen_brackets' 2*1+!10
(("[[";0)
("[][]";1)
("][][]]";0)
("[[][[][]";0)
("][]][[[[[[";0)
("]]][[]][]]][";0)
("[[[]][[[][[[][";0)
("[[]][[[]][]][][]";1)
("][[][[]]][[]]]][][";0)
("]][[[[]]]][][][[]]]]";0))
Klingphix
"[[]][]]"
%acc 0 !acc
%flag false !flag
len [
get tochar dup
"[" == [$acc 1 + !acc] if
"]" == [$acc 1 - !acc] if
$acc 0 < [true !flag] if
] for
print
$acc 0 # $flag or ( [" is NOT ok"] [" is OK"] ) if
print
" " input
Kotlin
import java.util.Random
fun isBalanced(s: String): Boolean {
if (s.isEmpty()) return true
var countLeft = 0 // number of left brackets so far unmatched
for (c in s) {
if (c == '[') countLeft++
else if (countLeft > 0) countLeft--
else return false
}
return countLeft == 0
}
fun main(args: Array<String>) {
println("Checking examples in task description:")
val brackets = arrayOf("", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]")
for (b in brackets) {
print(if (b != "") b else "(empty)")
println("\t " + if (isBalanced(b)) "OK" else "NOT OK")
}
println()
println("Checking 7 random strings of brackets of length 8:")
val r = Random()
(1..7).forEach {
var s = ""
for (j in 1..8) {
s += if (r.nextInt(2) == 0) '[' else ']'
}
println("$s " + if (isBalanced(s)) "OK" else "NOT OK")
}
}
Sample output (last 7 lines random) :
- Output:
Checking examples in task description: (empty) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK Checking 7 random strings of brackets of length 8: [[[[]]][ NOT OK [][[][]] OK [[[[[]]] NOT OK [[[[[]]] NOT OK [[[]]][] OK ]]]][[][ NOT OK ]][]][][ NOT OK
L++
(include "string")
(defn bool balanced (std::string s)
(def bal 0)
(foreach c s
(if (== c #\[) (++ bal)
(if (== c #\]) (-- bal)))
(if (< bal 0) (return false)))
(return (== bal 0)))
(main
(decl std::string (at tests) |{"", "[]", "[][]", "[[][]]", "][", "][][", "[]][[]"}|)
(pr std::boolalpha)
(foreach x tests
(prn x "\t" (balanced x))))
Lasso
define randomparens(num::integer,open::string='[',close::string=']') => {
local(out) = array
with i in 1 to #num do {
#out->insert(']', integer_random(1,#out->size || 1))
#out->insert('[', integer_random(1,#out->size || 1))
}
return #out->join
}
define validateparens(input::string,open::string='[',close::string=']') => {
local(i) = 0
#input->foreachcharacter => {
#1 == #open ? #i++
#1 == #close && --#i < 0 ? return false
}
return #i == 0 ? true | false
}
with i in 1 to 10
let input = randomparens(#i)
select #input + ' = ' + validateparens(#input)
- Output:
[] = true ][[] = false ]][[[] = false ][][[][] = false [[[]][[]]] = true ]]]][[[[][[] = false [[[[[[]]]]]][] = true [[]][][]][]][[[] = false [[[]][[[]][]]][[]] = true
Liberty BASIC
print "Supplied examples"
for i =1 to 7
read test$
print "The string '"; test$; "' is "; validString$( test$)
next i
print
data "", "[]", "][","[][]","][][","[[][]]","[]][[]"
print "Random generated examples"
for example =1 to 10
test$ =generate$( int( 1 +10 *rnd(1)))
print "The string '"; test$; "' is "; validString$( test$)
next example
end
function validString$( in$)
if left$( in$, 1) <>"[" and len( test$) <>0 then
validString$ ="not OK. Opens wrongly."
exit function
end if
paired =0
for i =1 to len( in$)
c$ =mid$( in$, i, 1)
if c$ ="[" then paired =paired +1
if c$ ="]" then paired =paired -1
if paired <0 then
exit for
end if
next i
if ( lBr =rBr) and ( paired >=0) then validString$ ="OK." else validString$ ="not OK. Unbalanced."
end function
function generate$( N)
lBr =0
rBr =0
' choose at random until N of one type generated
while ( lBr <N) and ( rBr <N)
select case int( 1.5 +rnd( 1))
case 1
lBr =lBr +1
generate$ =generate$ +"["
case 2
rBr =rBr +1
generate$ =generate$ +"]"
end select
wend
' now pad with the remaining other brackets
if lBr =N then
generate$ =generate$ +string$( N -rBr, "]")
else
generate$ =generate$ +string$( N -lBr, "[")
end if
end function
function string$( n, c$)
for i =1 to n
op$ =op$ +c$
next i
string$ =op$
end function
endSupplied examples The string is OK. The string '[]' is OK. The string '][' is not OK. Unbalanced. The string '[][]' is OK. The string '][][' is not OK. Unbalanced. The string '[[][]]' is OK. The string '[]][[]' is not OK. Unbalanced.
Random generated examples The string '[[][[[][]]]]' is OK. The string ']]]][[[[' is not OK. Unbalanced. The string '[[]][]' is OK. The string '[][[][[]][]]' is OK. The string '][[[]]][][' is not OK. Unbalanced. The string ']]]]][[[[[' is not OK. Unbalanced. The string '[[[]]]' is OK. The string ']][][[' is not OK. Unbalanced. The string '[[]]][][[][]' is not OK. Unbalanced. The string '][[][[][][]]][[]' is not OK. Unbalanced.
Lua
function isBalanced(s)
--Lua pattern matching has a 'balanced' pattern that matches sets of balanced characters.
--Any two characters can be used.
return s:gsub('%b[]','')=='' and true or false
end
function randomString()
math.randomseed(os.time())
math.random()math.random()math.random()math.random()
local tokens={'[',']'}
local result={}
for i=1,8 do
table.insert(result,tokens[math.random(1,2)])
end
return table.concat(result)
end
local RS=randomString()
print(RS)
print(isBalanced(RS))
M2000 Interpreter
module Balanced_brackets{
// Generate a string with N opening brackets [ and with N closing brackets ], in some arbitrary order.
function randomBrackets(max as long) {
if max<1 then max=1
def putbracket()=mid$("[[[[]]",random(1,6),1)
dim a(random(1, max)) as string<<putbracket()
=a()#str$("")
}
// Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.
function check(s as string) {
long i, level
for i=1 to len(s)
if mid$(s,i,1)="[" then level++ else level--
if level<0 then exit for
next
=level=0
}
string k
boolean m
do
k=randomBrackets(10)
m=check(k)
print k;@(12);": ";if$(m->"OK", "NOT OK")
until m
}
Balanced_brackets- Output:
[[[] : NOT OK [[][]] : OK
Maple
This functionality is provided by Maple.
> use StringTools in
> IsBalanced( "", "[", "]" );
> IsBalanced( "[", "[", "]" );
> IsBalanced( "]", "[", "]" );
> IsBalanced( "[]", "[", "]" );
> IsBalanced( "][", "[", "]" );
> IsBalanced( "[][]", "[", "]" );
> IsBalanced( "[[][]]", "[", "]" );
> IsBalanced( "[[[]][]]]", "[", "]" );
> s := Random( 20, "[]" );
> IsBalanced( s, "[", "]" )
> end use;
true
false
false
true
false
true
true
false
s := "[[]][[[[[[[[[]][][]]"
falseFurthermore, Maple can check whether multiple fences are balanced in the same string.
> StringTools:-IsBalanced( "[()()]", "[(", "])" );
trueMathematica /Wolfram Language
(* Generate open/close events. *)
gen[n_] := RandomSample[Table[{1, -1}, {n}] // Flatten]
(* Check balance. *)
check[lst_] := And @@ (# >= 0 & /@ Accumulate[lst])
(* Do task for string with n opening and n closing brackets. *)
doString[n_] := (
lst = gen[n];
str = StringJoin[lst /. {1 -> "[", -1 -> "]"}];
Print[str <> If[match[lst, 0],
" is balanced.",
" is not balanced."]])
MATLAB / Octave
function x = isbb(s)
t = cumsum((s=='[') - (s==']'));
x = all(t>=0) && (t(end)==0);
end;
Output:
octave:9> isbb('[]')
ans = 1
octave:10> isbb('][')
ans = 0
octave:11> isbb('][][')
ans = 0
octave:12> isbb('[][]')
ans = 1
octave:13> isbb('[][][]')
ans = 1
octave:14> isbb('[]][[]')
ans = 0
Maxima
brack(s) := block(
[n: slength(s), r: 0, c],
catch(
for i thru n do (
if cequal(c: charat(s, i), "]") then (if (r: r - 1) < 0 then throw(false))
elseif cequal(c, "[") then r: r + 1
),
is(r = 0)
)
)$
brack("");
true
brack("[");
false
brack("]");
false
brack("[]");
true
brack("][");
false
brack("[[][]]");
true
brack("[[[]][]]]");
false
Mercury
:- module balancedbrackets.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- import_module list, random, char.
:- pred brackets(int::in,list(char)::out,supply::mdi,supply::muo) is det.
:- pred imbalance(list(char)::in,int::out) is semidet.
:- pred balanced(list(char)::in) is semidet.
:- implementation.
:- import_module int.
imbalance([],0).
imbalance(['['|T],N) :- imbalance(T,N+1).
imbalance([']'|T],N) :- N > 0, imbalance(T,N-1).
balanced(S) :- imbalance(S,0).
brackets(N,S,!RS) :-
(
N < 1 -> S is []
; random(0,2,R,!RS),
( R is 0 -> S is ['['|T], brackets(N-1,T,!RS)
; S is [']'|T], brackets(N-1,T,!RS))).
main(!IO) :-
random.init(0,RS),
brackets(4,S,RS,_),
print(S,!IO),
(
balanced(S) -> print(" is balanced\n",!IO)
; print(" is unbalanced\n", !IO)
).MiniScript
We start by defining a function:
isBalanced = function(str)
level = 0
for c in str
if c == "[" then level = level + 1
if c == "]" then level = level - 1
if level < 0 then return false
end for
return level == 0
end function
We can evaluate the example strings with this code:
examples = [
"",
"[]",
"[][]",
"[[][]]",
"][",
"][][",
"[]][[]",
"[[[]"]
for str in examples
balanced = isBalanced(str)
if balanced then outcome = "is OK" else outcome = "NOT OK"
print """" + str + """ " + outcome
end for
- Output:
"" is OK "[]" is OK "[][]" is OK "[[][]]" is OK "][" NOT OK "][][" NOT OK "[]][[]" NOT OK "[[[]" NOT OK
Modula-2
An interesting point is how to ensure that all strings of N left plus N right brackets are equally likely. The program below shows one way of doing this.
MODULE Brackets;
IMPORT IO, Lib;
CONST MaxN = 4;
PROCEDURE DoTest( N : CARDINAL);
VAR
brStr : ARRAY [0..2*MaxN] OF CHAR; (* string of brackets *)
verdict : ARRAY [0..2] OF CHAR;
br : CHAR;
k, nL, nR, randNum : CARDINAL;
count : INTEGER;
BEGIN
k := 0; (* index into brStr *)
nL := N; nR := N; (* number of left/right brackets remaining *)
WHILE (nL > 0) AND (nR > 0) DO
randNum := Lib.RANDOM( nL + nR);
IF (randNum < nL) THEN brStr[k] := '['; DEC(nL);
ELSE brStr[k] := ']'; DEC(nR); END;
INC(k);
END;
(* Here when only one kind of bracket is possible *)
IF (nL = 0) THEN br := ']' ELSE br := '['; END;
WHILE (k < 2*N) DO brStr[k] := br; INC(k); END;
brStr[k] := 0C; (* null to mark end of string *)
(* Test for balance *)
count := 0;
k := 0;
REPEAT
IF brStr[k] = '[' THEN INC( count) ELSE DEC( count) END;
INC( k);
UNTIL (count < 0) OR (k = 2*N);
IF (count < 0) THEN verdict := 'no' ELSE verdict := 'yes' END;
IO.WrStr( brStr); IO.WrStr(' '); IO.WrStr( verdict);
IO.WrLn;
END DoTest;
(* Main routine *)
VAR
j : CARDINAL;
BEGIN
Lib.RANDOMIZE;
FOR j := 1 TO 10 DO
DoTest( Lib.RANDOM(MaxN) + 1);
END;
END Brackets.
- Output:
[]][[]][ no [[[]]] yes ][ no ][]][[ no [][[]] yes ][[] no [][] yes ][][]][[ no [] yes []][[][] no
Nanoquery
import Nanoquery.Util
def gen(N)
txt = {"[", "]"} * N
txt = new(Random).shuffle(txt)
return "".join("", txt)
end
def balanced(txt)
braced = 0
for ch in txt
if ch = "["
braced += 1
else if ch = "]"
braced -= 1
end
if braced < 0
return false
end
end
return braced = 0
end
// unlike Python, the range function is inclusive in Nanoquery
for N in range(1, 10)
txt = gen(N)
if balanced(txt)
println format("%-22s is balanced", txt)
else
println format("%-22s is not balanced", txt)
end
end- Output:
is balanced [] is balanced [][] is balanced []][][ is not balanced []][[[]] is not balanced [][[[[]]]] is balanced ][[]][][]][[ is not balanced ][]][[][]][[[] is not balanced [[]][[[]][]][]][ is not balanced [[][[]][][]]][[[]] is not balanced [[][][[[][]][[]]][]] is balanced
Nim
from random import random, randomize, shuffle
from strutils import repeat
randomize()
proc gen(n: int): string =
result = "[]".repeat(n)
shuffle(result)
proc balanced(txt: string): bool =
var b = 0
for c in txt:
case c
of '[':
inc(b)
of ']':
dec(b)
if b < 0: return false
else: discard
b == 0
for n in 0..9:
let s = gen(n)
echo "'", s, "' is ", (if balanced(s): "balanced" else: "not balanced")
Output:
'' is balanced '][' is not balanced '][[]' is not balanced '[][[]]' is balanced '[[]][][]' is balanced ']][][[[][]' is not balanced '][]][][][[][' is not balanced '[[[[[[]]]][]]]' is balanced '][[][]]]][[[[][]' is not balanced '][][][][][[][[]]][' is not balanced
Nu
def gen_brackets [n: int] { 1..$in | each {["[" "]"]} | flatten | shuffle | str join }
def check_brackets [] {
split chars | reduce --fold 0 {|x, d|
if ($d < 0) {-1} else {
$d + (if ($x == "[") {1} else {-1})
}
} | $in > -1
}
1..10 | each {gen_brackets $in | {brackets: $in, valid: ($in | check_brackets)}} | print- Output:
╭───┬──────────────────────┬───────╮ │ # │ brackets │ valid │ ├───┼──────────────────────┼───────┤ │ 0 │ ][ │ false │ │ 1 │ []][ │ false │ │ 2 │ [[][]] │ true │ │ 3 │ [[[][]]] │ true │ │ 4 │ ]]][[[[][] │ false │ │ 5 │ [][][][[[]]] │ true │ │ 6 │ ]]]]][]][[[[[[ │ false │ │ 7 │ ][[][]]]][[][[[] │ false │ │ 8 │ []]]][][][[][]][[[ │ false │ │ 9 │ ][][][[[[[]]]][[]][] │ false │ ╰───┴──────────────────────┴───────╯
Oberon-2
MODULE BalancedBrackets;
IMPORT
Object,
Object:Boxed,
ADT:LinkedList,
ADT:Storable,
IO,
Out := NPCT:Console;
TYPE
(* CHAR is not boxed in the standard lib *)
(* so make a boxed char *)
Character* = POINTER TO CharacterDesc;
CharacterDesc* = RECORD
(Boxed.ObjectDesc)
c: CHAR;
END;
(* Method for a boxed char *)
PROCEDURE (c: Character) INIT*(x: CHAR);
BEGIN
c.c := x;
END INIT;
PROCEDURE NewCharacter*(c: CHAR): Character;
VAR
x: Character;
BEGIN
NEW(x);x.INIT(c);RETURN x
END NewCharacter;
PROCEDURE (c: Character) ToString*(): STRING;
BEGIN
RETURN Object.NewLatin1Char(c.c);
END ToString;
PROCEDURE (c: Character) Load*(r: Storable.Reader) RAISES IO.Error;
BEGIN
r.ReadChar(c.c);
END Load;
PROCEDURE (c: Character) Store*(w: Storable.Writer) RAISES IO.Error;
BEGIN
w.WriteChar(c.c);
END Store;
PROCEDURE (c: Character) Cmp*(o: Object.Object): LONGINT;
BEGIN
IF c.c < o(Character).c THEN RETURN -1
ELSIF c.c = o(Character).c THEN RETURN 0
ELSE RETURN 1
END
END Cmp;
(* end of methods for a boxed char *)
PROCEDURE CheckBalance(str: STRING): BOOLEAN;
VAR
s: LinkedList.LinkedList(Character);
chars: Object.CharsLatin1;
n, x: Boxed.Object;
i,len: LONGINT;
BEGIN
i := 0;
chars := str(Object.String8).CharsLatin1();
len := str.length;
s := NEW(LinkedList.LinkedList(Character));
WHILE (i < len) & (chars[i] # 0X) DO
IF s.IsEmpty() THEN
s.Append(NewCharacter(chars[i])) (* Push character *)
ELSE
n := s.GetLast(); (* top character *)
WITH
n: Character DO
IF (chars[i] = ']') & (n.c = '[') THEN
x := s.RemoveLast(); (* Pop character *)
x := NIL
ELSE
s.Append(NewCharacter(chars[i]))
END
ELSE RETURN FALSE
END (* WITH *)
END;
INC(i)
END;
RETURN s.IsEmpty()
END CheckBalance;
PROCEDURE Do;
VAR
str: STRING;
BEGIN
str := "[]";Out.String(str + ":> "); Out.Bool(CheckBalance(str));Out.Ln;
str := "[][]";Out.String(str + ":> ");Out.Bool(CheckBalance(str));Out.Ln;
str := "[[][]]";Out.String(str + ":> ");Out.Bool(CheckBalance(str));Out.Ln;
str := "][";Out.String(str + ":> ");Out.Bool(CheckBalance(str));Out.Ln;
str := "][][";Out.String(str + ":> ");Out.Bool(CheckBalance(str));Out.Ln;
str := "[]][[]";Out.String(str + ":> ");Out.Bool(CheckBalance(str));Out.Ln;
END Do;
BEGIN
Do
END BalancedBrackets.
- Output:
[]:> TRUE [][]:> TRUE [[][]]:> TRUE ][:> FALSE ][][:> FALSE []][[]:> FALSE
Objeck
bundle Default {
class Balanced {
function : IsBalanced(text : String) ~ Bool {
level := 0;
each(i : text) {
character := text->Get(i);
if(character = ']') {
if(level = 0) {
return false;
};
level -= 1;
};
if(character = '[') {
level += 1;
};
};
return level = 0;
}
function : Main(args : String[]) ~ Nil {
": "->Print(); IsBalanced("")->PrintLine();
"[]: "->Print(); IsBalanced("[]")->PrintLine();
"[][]: "->Print(); IsBalanced("[][]")->PrintLine();
"[[][]]: "->Print(); IsBalanced("[[][]]")->PrintLine();
"][: "->Print(); IsBalanced("][")->PrintLine();
"][][: "->Print(); IsBalanced("][][")->PrintLine();
"[]][[]: "->Print(); IsBalanced("[]][[]")->PrintLine();
}
}
}: true []: true [][]: true [[][]]: true ][: false ][][: false []][[]: false
OCaml
let generate_brackets n =
let rec aux i acc =
if i <= 0 then acc else
aux (pred i) ('['::']'::acc)
in
let brk = aux n [] in
List.sort (fun _ _ -> (Random.int 3) - 1) brk
let is_balanced brk =
let rec aux = function
| [], 0 -> true
| '['::brk, level -> aux (brk, succ level)
| ']'::brk, 0 -> false
| ']'::brk, level -> aux (brk, pred level)
| _ -> assert false
in
aux (brk, 0)
let () =
let n = int_of_string Sys.argv.(1) in
Random.self_init();
let brk = generate_brackets n in
List.iter print_char brk;
Printf.printf " %B\n" (is_balanced brk);
;;
$ ocaml balanced_brackets.ml 3 []][[] false $ ocaml balanced_brackets.ml 3 [[]][] true
Oforth
String method: isBalanced
| c |
0 self forEach: c [
c '[' == ifTrue: [ 1+ continue ]
c ']' <> ifTrue: [ continue ]
1- dup 0 < ifTrue: [ drop false return ]
]
0 == ;
: genBrackets(n)
"" #[ "[" "]" 2 rand 2 == ifTrue: [ swap ] rot + swap + ] times(n) ;- Output:
#[ genBrackets(5) dup print " -->" print isBalanced println ] times(10) [[][[]][]] -->-1 ][][][][][ -->0 ][[][][]][ -->0 ][[]][[]][ -->0 [][][][][] -->-1 ]]][][][[[ -->0 [[[[[]]]]] -->-1 [[[[[]]]]] -->-1 ][][][][][ -->0 ]]][][][[[ -->0
ooRexx
tests = .array~of("", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]")
-- add some randomly generated tests
loop i = 1 to 8
tests~append(generateBrackets(i))
end
loop test over tests
say test":" checkbrackets(test)
end
::routine checkBrackets
use arg input
-- counter of bracket groups. Must be 0 at end to be valid
groups = 0
-- loop over all of the characters
loop c over input~makearray("")
if c == '[' then groups += 1
else if c == ']' then groups -= 1
else return .false -- non-bracket char found
-- check for a close occurring before an open
if groups < 0 then return .false
end
-- should be zero at the end
return groups == 0
-- generate a string with n pairs of brackets
::routine generateBrackets
use arg n
answer = .mutablebuffer~new(,2*n)
openBracketsNeeded = n
unclosedBrackets = 0
loop while answer~length < 2 * n
if random(0, 1) & openBracketsNeeded > 0 | unclosedBrackets == 0 then do
answer~append('[')
openBracketsNeeded -= 1
unclosedBrackets += 1
end
else do
answer~append(']')
unclosedBrackets -= 1
end
end
return answer~string
Sample output (uses randomly generated groupings, so it should be different on each run):
: 1 []: 1 ][: 0 [][]: 1 ][][: 0 [[][]]: 1 []][[]: 0 []: 1 [[]]: 1 [][[]]: 1 [][[][]]: 1 [][][[[]]]: 1 [[]][[][]][]: 1 [][][[][[][]]]: 1 [][[][][[[][]]]]: 1
OxygenBasic
function CheckBrackets(string s) as bool
'=======================================
sys co, le=len s
byte b at strptr s
indexbase 0
for i=0 to <le
select b(i)
case "[" : co++
case "]" : co--
end select
if co<0 then return 0
next
if co=0 then return 1
end function
'TEST
'====
print CheckBrackets "" '1
print CheckBrackets "[" '0
print CheckBrackets "]" '0
print CheckBrackets "[]" '1
print CheckBrackets "[[]" '0
print CheckBrackets "[]]" '0
print CheckBrackets "[][]"'1
print CheckBrackets "][" '0PARI/GP
balanced(s)={
my(n=0,v=Vecsmall(s));
for(i=1,#v,
if(v[i]==91,
n++
,
if(v[i]==93 && n, n--, return(0))
)
);
!n
};
rnd(n)=Strchr(vectorsmall(n,i,if(random(2),91,93)))
forstep(n=0,10,2,s=rnd(n);print(s"\t"if(balanced(s),"true","false")))Pascal
See Delphi
PascalABC.NET
function GenBracketExpr(n: integer): string;
begin
var a := Arr('[',']')*n;
Shuffle(a);
Result := a.JoinToString
end;
function IsBalanced(s: string): boolean;
begin
Result := True;
var st := new Stack<char>;
foreach var c in s do
if c = '[' then
st.Push(c)
else if (st.Count > 0) and (st.Peek = '[') then
st.Pop
else begin
Result := False;
exit
end;
end;
begin
loop 10 do
begin
var s := GenBracketExpr(Random(2,5));
Println(s, IsBalanced(s));
end;
end.
- Output:
[][] True [[][]] True ]]][[[]][[ False [[[]]] True ]][][[[] False []]][[ False [][]]][[][ False [[][[][]]] True [][][][] True [[]][[[]]] True
Perl
Idiomatic solution, using a regex that performs subpattern recursion (works with Perl 5.10 and newer):
sub generate {
my $n = shift;
my $str = '[' x $n;
substr($str, rand($n + $_), 0) = ']' for 1..$n;
return $str;
}
sub balanced {
shift =~ /^ (\[ (?1)* \])* $/x;
}
for (0..8) {
my $input = generate($_);
print balanced($input) ? " ok:" : "bad:", " '$input'\n";
}
- Output:
ok: '' ok: '[]' bad: '[]][' bad: ']][][[' ok: '[[]][[]]' bad: '[[[][]]]][' bad: '][[[]][]][[]' ok: '[[]][[[][[]]]]' bad: ']][]]][[][][[][['
If input strings are allowed to contain unrelated characters, this can be extended to:
sub balanced {
shift =~ /^ ( [^\[\]]++ | \[ (?1)* \] )* $/x;
}
Regexp::Common::balanced can give such a regexp too (here via a subroutine call)
use Regexp::Common 'RE_balanced';
sub balanced {
return shift =~ RE_balanced(-parens=>'[]')
}
Alternative implementation, using straightforward depth counting:
sub balanced {
my $depth = 0;
for (split //, shift) {
if ($_ eq '[') { ++$depth }
elsif ($_ eq ']') { return if --$depth < 0 }
}
return !$depth
}
Phix
with javascript_semantics function check_brackets(sequence s) integer level = 0 for i=1 to length(s) do switch s[i] case '[': level += 1 case ']': level -= 1 if level<0 then return false end if end switch end for return (level=0) end function sequence s constant ok = {"not ok","ok"} for i=1 to 10 do for j=1 to 2 do s = shuffle(join(repeat("[]",i-1),"")) printf(1,"%s %s\n",{s,ok[check_brackets(s)+1]}) end for end for
- Output:
ok ok [] ok ][ not ok [][] ok ][][ not ok []][][ not ok ][][[] not ok ][[][]][ not ok [][[][]] ok []]][[[]][ not ok ][]][[[]][ not ok ][[]]]][[][[ not ok [][[]][[]][] ok []][][]]][[[[] not ok [[][][]][][[]] ok [[][]][][[]][[]] ok ][][[[[][]]][]][ not ok [[[[]]][][[[][]]]] ok [[[]]][[[[][]]][]] ok
Phixmonti
"[[]][]"
0 var acc
len for
get dup
'[' == if acc 1 + var acc endif
']' == if acc 1 - var acc endif
acc 0 < if exitfor endif
endfor
print
acc 0 < if
" is NOT ok"
else
" is OK"
endif
printPHP
The sample is given as unix shell script, you need to have php-cli (or what your package manager calls it) installed.
#!/usr/bin/php
<?php
# brackets generator
function bgenerate ($n) {
if ($n==0) return '';
$s = str_repeat('[', $n) . str_repeat(']', $n);
return str_shuffle($s);
}
function printbool($b) {return ($b) ? 'OK' : 'NOT OK';}
function isbalanced($s) {
$bal = 0;
for ($i=0; $i < strlen($s); $i++) {
$ch = substr($s, $i, 1);
if ($ch == '[') {
$bal++;
} else {
$bal--;
}
if ($bal < 0) return false;
}
return ($bal == 0);
}
# test parameters are N (see spec)
$tests = array(0, 2,2,2, 3,3,3, 4,4,4,4);
foreach ($tests as $v) {
$s = bgenerate($v);
printf("%s\t%s%s", $s, printbool(isbalanced($s)), PHP_EOL);
}
Sample run:
OK [][] OK [[]] OK []][ NOT OK ][][[] NOT OK [][[]] OK ][[[]] NOT OK ]][[][][ NOT OK []][][[] NOT OK ][]]][[[ NOT OK [[[][]]] OK
Picat
Foreach loop
go1 ?=>
tests(Tests),
member(Test,Tests),
printf("%s: ", Test),
( balanced_brackets(Test) ->
println("OK")
;
println("NOT OK")
),
fail,
nl.
go1 => true.
% Check if a string of [] is balanced
balanced_brackets(B) =>
C = 0,
foreach(I in 1..B.length, C >= 0)
C:= C + cond(B[I] = '[', 1, -1)
end,
C == 0.
tests(["","[]", "[][]", "[[][]]", "][",
"][][", "[]][[]", "[][][][][][][][][][]",
"[[[[[[[]]]]]]]", "[[[[[[[]]]]]]",
"[][[]][]","[[][]][]", "[][][[]][]"]).- Output:
: OK []: OK [][]: OK [[][]]: OK ][: NOT OK ][][: NOT OK []][[]: NOT OK [][][][][][][][][][]: OK [[[[[[[]]]]]]]: OK [[[[[[[]]]]]]: NOT OK [][[]][]: OK [[][]][]: OK [][][[]][]: OK
DCG
Here is an implementation using DCG (Definite Clause Grammars).
go_dcg ?=>
tests(Tests),
foreach(Test in Tests)
printf("%s: ", Test),
if balanced(Test,[]) then
println("OK")
else
println("NOT OK")
end
end,
nl.
go_dcg => true.
balanced --> "".
balanced --> "[", balanced, "]", balanced.PicoLisp
(load "@lib/simul.l") # For 'shuffle'
(de generateBrackets (N)
(shuffle (make (do N (link "[" "]")))) )
(de checkBrackets (S)
(let N 0
(for C S
(if (= C "[")
(inc 'N)
(if2 (= C "]") (=0 N)
(off N)
(dec 'N) ) ) )
(=0 N) ) )
(for N 10
(prinl (if (checkBrackets (prin (generateBrackets N))) " OK" "not OK")) )Output:
[] OK [[]] OK ]]][[[not OK [[[][]]] OK [][][[[]]] OK []][[[][[]]]not OK [[[]]][][][][] OK ]][][[[[]][]]][[not OK []][][[[][[]]][]][not OK [[[][]]]]][][[]]][[[not OK
PL/I
*process m or(!) s attributes source;
cb: Proc Options(main);
/* PL/I program to check for balanced brackets [] ********************
* 07.12.2013 Walter Pachl translated from REXX Version 2
*********************************************************************/
Dcl v Char(20) Var;
Dcl (i,j) Bin Fixed(31);
Dcl r Bin Float(53);
Call testbal(''); /* first some user written tests */
Call testbal('[][][][[]]');
Call testbal('[][][][[]]][');
Call testbal('[');
Call testbal(']');
Call testbal('[]');
Call testbal('][');
Call testbal('][][');
Call testbal('[[]]');
Call testbal('[[[[[[[]]]]]]]');
Call testbal('[[[[[]]]][]');
Call testbal('[][]');
Call testbal('[]][[]');
Call testbal(']]][[[[]');
Call testbal('[[a]][b]');
Put Edit(' ')(Skip,a);
r=random(12345); /* then some generated ones */
Do i=1 To 10;
v='';
Do j=1 To 10;
r=random();
If r>0.5 Then v=v!!']';
Else v=v!!'[';
End;
Call testbal(v);
End;
Return;
testbal: Proc(s); /* test the given string and show result */
Dcl s Char(*);
Dcl yesno(0:1) Char(20) Var Init('unbalanced',' balanced');
Put Edit(yesno(checkbal(s)),''''!!s!!'''')(Skip,a,x(1),a);
End;
checkBal: proc(s) Returns(Bin Fixed(31));
/*check for balanced brackets [] */
Dcl s Char(*);
Dcl nest Bin Fixed(31) Init(0);
Dcl i Bin Fixed(31);
Do i=1 To length(s);
Select(substr(s,i,1));
When('[') nest+=1;
When(']') Do;
If nest=0 Then return(0);
nest-=1;
End;
Otherwise;
End;
End;
Return(nest=0);
End;
End;Output:
balanced '' balanced '[][][][[]]' unbalanced '[][][][[]]][' unbalanced '[' unbalanced ']' balanced '[]' unbalanced '][' unbalanced '][][' balanced '[[]]' balanced '[[[[[[[]]]]]]]' unbalanced '[[[[[]]]][]' balanced '[][]' unbalanced '[]][[]' unbalanced ']]][[[[]' balanced '[[a]][b]' unbalanced '][[][[[[[]' balanced '[[]][[[]]]' unbalanced ']][[[[][[[' unbalanced '[[[][][[]]' unbalanced ']]][[[[[]]' balanced '[[[][][]]]' unbalanced '[][][][[][' unbalanced '[[]]]][[][' unbalanced '[]][]]][[]' unbalanced '][[][[[[[]'
PowerShell
function Get-BalanceStatus ( $String )
{
$Open = 0
ForEach ( $Character in [char[]]$String )
{
switch ( $Character )
{
"[" { $Open++ }
"]" { $Open-- }
default { $Open = -1 }
}
# If Open drops below zero (close before open or non-allowed character)
# Exit loop
If ( $Open -lt 0 ) { Break }
}
$Status = ( "NOT OK", "OK" )[( $Open -eq 0 )]
return $Status
}# Test
$Strings = @( "" )
$Strings += 1..5 | ForEach { ( [char[]]("[]" * $_) | Get-Random -Count ( $_ * 2 ) ) -join "" }
ForEach ( $String in $Strings )
{
$String.PadRight( 12, " " ) + (Get-BalanceStatus $String)
}- Output:
OK [] OK ]][[ NOT OK ]][][[ NOT OK [[[][]]] OK ][[[]][][] NOT OK
PowerShell (Regex Version)
function Test-BalancedBracket
{
<#
.SYNOPSIS
Tests a string for balanced brackets.
.DESCRIPTION
Tests a string for balanced brackets. ("<>", "[]", "{}" or "()")
.EXAMPLE
Test-BalancedBracket -Bracket Brace -String '{abc(def[0]).xyz}'
Test a string for balanced braces.
.EXAMPLE
Test-BalancedBracket -Bracket Curly -String '{abc(def[0]).xyz}'
Test a string for balanced curly braces.
.EXAMPLE
Test-BalancedBracket -Bracket Curly -String ([System.IO.File]::ReadAllText('.\Foo.ps1'))
Test a file for balanced curly braces.
.LINK
http://go.microsoft.com/fwlink/?LinkId=133231
#>
[CmdletBinding()]
[OutputType([bool])]
Param
(
[Parameter(Mandatory=$true)]
[ValidateSet("Angle", "Brace", "Curly", "Paren")]
[string]
$Bracket,
[Parameter(Mandatory=$true)]
[AllowEmptyString()]
[string]
$String
)
$notFound = -1
$brackets = @{
Angle = @{Left="<"; Right=">"; Regex="^[^<>]*(?>(?>(?'pair'\<)[^<>]*)+(?>(?'-pair'\>)[^<>]*)+)+(?(pair)(?!))$"}
Brace = @{Left="["; Right="]"; Regex="^[^\[\]]*(?>(?>(?'pair'\[)[^\[\]]*)+(?>(?'-pair'\])[^\[\]]*)+)+(?(pair)(?!))$"}
Curly = @{Left="{"; Right="}"; Regex="^[^{}]*(?>(?>(?'pair'\{)[^{}]*)+(?>(?'-pair'\})[^{}]*)+)+(?(pair)(?!))$"}
Paren = @{Left="("; Right=")"; Regex="^[^()]*(?>(?>(?'pair'\()[^()]*)+(?>(?'-pair'\))[^()]*)+)+(?(pair)(?!))$"}
}
if ($String.IndexOf($brackets.$Bracket.Left) -eq $notFound -and
$String.IndexOf($brackets.$Bracket.Right) -eq $notFound -or $String -eq [String]::Empty)
{
return $true
}
$String -match $brackets.$Bracket.Regex
}
'', '[]', '][', '[][]', '][][', '[[][]]', '[]][[]' | ForEach-Object {
if ($_ -eq "") { $s = "(Empty)" } else { $s = $_ }
"{0}: {1}" -f $s.PadRight(8), "$(if (Test-BalancedBracket Brace $s) {'Is balanced.'} else {'Is not balanced.'})"
}- Output:
(Empty) : Is balanced. [] : Is balanced. ][ : Is not balanced. [][] : Is balanced. ][][ : Is not balanced. [[][]] : Is balanced. []][[] : Is not balanced.
Prolog
DCG are very usefull for this kind of exercice !
rosetta_brackets :-
test_brackets([]),
test_brackets(['[',']']),
test_brackets(['[',']','[',']']),
test_brackets(['[','[',']','[',']',']']),
test_brackets([']','[']),
test_brackets([']','[',']','[']),
test_brackets(['[',']',']','[','[',']']).
balanced_brackets :-
gen_bracket(2, B1, []), test_brackets(B1),
gen_bracket(4, B2, []), test_brackets(B2),
gen_bracket(4, B3, []), test_brackets(B3),
gen_bracket(6, B4, []), test_brackets(B4),
gen_bracket(6, B5, []), test_brackets(B5),
gen_bracket(8, B6, []), test_brackets(B6),
gen_bracket(8, B7, []), test_brackets(B7),
gen_bracket(10, B8, []), test_brackets(B8),
gen_bracket(10, B9, []), test_brackets(B9).
test_brackets(Goal) :-
( Goal = [] -> write('(empty)'); maplist(write, Goal)),
( balanced_brackets(Goal, []) ->
writeln(' succeed')
;
writeln(' failed')
).
% grammar of balanced brackets
balanced_brackets --> [].
balanced_brackets -->
['['],
balanced_brackets,
[']'].
balanced_brackets -->
['[',']'],
balanced_brackets.
% generator of random brackets
gen_bracket(0) --> [].
gen_bracket(N) -->
{N1 is N - 1,
R is random(2)},
bracket(R),
gen_bracket(N1).
bracket(0) --> ['['].
bracket(1) --> [']'].Sample output :
?- balanced_brackets. [[ failed [[][ failed [[]] succeed [[][]] succeed [][[][ failed ][]][[[] failed [[[[]][] failed [[[[[][[]] failed []][[[][]] failed true .
Test with Rosetta examples :
?- rosetta_brackets. (empty) succeed [] succeed [][] succeed [[][]] succeed ][ failed ][][ failed []][[] failed true.
PureBasic
Procedure.s Generate(N)
For i=1 To N
sample$+"[]"
Next
For i=Len(sample$)-1 To 2 Step -1
r=Random(i-1)+1
If r<>i
a.c=PeekC(@sample$+r*SizeOf(Character))
b.c=PeekC(@sample$+i*SizeOf(Character))
PokeC(@sample$+r*SizeOf(Character), b)
PokeC(@sample$+i*SizeOf(Character), a)
EndIf
Next
ProcedureReturn sample$
EndProcedure
Procedure Balanced(String$)
Protected *p.Character, cnt
*p=@String$
While *p\c
If *p\c='['
cnt+1
ElseIf *p\c=']'
cnt-1
If cnt<0: Break: EndIf
EndIf
*p+SizeOf(Character)
Wend
If cnt=0
ProcedureReturn #True
EndIf
EndProcedure
;- Test code
OpenConsole()
For i=1 To 5
TestString$ = Generate(i)
Print(TestString$)
If Balanced(TestString$)
PrintN(" is balanced.")
Else
PrintN(" is not balanced")
EndIf
NextOutput sample
[] is balanced. [[]] is balanced. [[[]]] is balanced. [][]]][[ is not balanced [][][][]][ is not balanced
Python
Procedural
>>> def gen(N):
... txt = ['[', ']'] * N
... random.shuffle( txt )
... return ''.join(txt)
...
>>> def balanced(txt):
... braced = 0
... for ch in txt:
... if ch == '[': braced += 1
... if ch == ']':
... braced -= 1
... if braced < 0: return False
... return braced == 0
...
>>> for txt in (gen(N) for N in range(10)):
... print ("%-22r is%s balanced" % (txt, '' if balanced(txt) else ' not'))
...
'' is balanced
'[]' is balanced
'[][]' is balanced
'][[[]]' is not balanced
'[]][[][]' is not balanced
'[][[][]]][' is not balanced
'][]][][[]][[' is not balanced
'[[]]]]][]][[[[' is not balanced
'[[[[]][]]][[][]]' is balanced
'][[][[]]][]]][[[[]' is not balancedFunctional
Rather than explicitly track the count, we can just write the per-element test and use stdlib functions to turn it into a whole-sequence test. It's straightforwardly declarative, and hard to get wrong, but whether it's actually easier to understand depends on how familiar the reader is with thinking in `itertools` style.
>>> from itertools import accumulate
>>> from random import shuffle
>>> def gen(n):
... txt = list('[]' * n)
... shuffle(txt)
... return ''.join(txt)
...
>>> def balanced(txt):
... brackets = ({'[': 1, ']': -1}.get(ch, 0) for ch in txt)
... return all(x>=0 for x in accumulate(brackets))
...
>>> for txt in (gen(N) for N in range(10)):
... print ("%-22r is%s balanced" % (txt, '' if balanced(txt) else ' not'))
...
'' is balanced
'][' is not balanced
'[]][' is not balanced
']][[[]' is not balanced
'][[][][]' is not balanced
'[[[][][]]]' is balanced
'][[[][][]][]' is not balanced
'][]][][[]][[][' is not balanced
'][[]]][][[]][[[]' is not balanced
'][[][[]]]][[[]][][' is not balancedArray Programming
The numpy library gives us a way to write just the elementwise tests and automatically turn them into whole-sequence tests, although it can be a bit clumsy to use for character rather than numeric operations. The simplicity of the final expression probably doesn't make up for all that extra clumsiness in this case.
>>> import numpy as np
>>> from random import shuffle
>>> def gen(n):
... txt = list('[]' * n)
... shuffle(txt)
... return ''.join(txt)
...
>>> m = np.array([{'[': 1, ']': -1}.get(chr(c), 0) for c in range(128)])
>>> def balanced(txt):
... a = np.array(txt, 'c').view(np.uint8)
... return np.all(m[a].cumsum() >= 0)
...
>>> for txt in (gen(N) for N in range(10)):
... print ("%-22r is%s balanced" % (txt, '' if balanced(txt) else ' not'))
...
'' is balanced
'][' is not balanced
'[[]]' is balanced
'[]][][' is not balanced
']][]][[[' is not balanced
'[[]][[][]]' is balanced
'[][[]][[]]][' is not balanced
'[][[[]][[]]][]' is balanced
'[[][][[]]][[[]]]' is balanced
'][]][][[]][]][][[[' is not balancedQi
(define balanced-brackets-0
[] 0 -> true
[] _ -> false
[#\[|R] Sum -> (balanced-brackets-0 R (+ Sum 1))
_ 0 -> false
[_ |R] Sum -> (balanced-brackets-0 R (- Sum 1)))
(define balanced-brackets
"" -> true
S -> (balanced-brackets-0 (explode (INTERN S)) 0))
(balanced-brackets "")
(balanced-brackets "[]")
(balanced-brackets "[][]")
(balanced-brackets "[[][]]")
(balanced-brackets "][")
(balanced-brackets "][][")
(balanced-brackets "[]][[]")Quackery
[ char [ over of
swap
char ] swap of
join shuffle ] is bracket$ ( n --> $ )
[ 0 swap witheach
[ char [ =
iff 1 else -1 +
dup 0 < if
conclude ]
0 = ] is balanced ( $ --> b )
10 times
[ 20 i 2 * - times sp
i bracket$ dup echo$
say " is "
balanced not if
[ say "un" ]
say "balanced."
cr ]- Output:
Full disclosure: it took quite a few attempts to randomly achieve a pleasing distribution of balanced and unbalanced strings.
[[][]][][][[]][][] is balanced.
[][]][][[]]][][[ is unbalanced.
[]][][]][[][[] is unbalanced.
[][[[[][]]]] is balanced.
]][[][][][ is unbalanced.
]][[][][ is unbalanced.
[][][] is balanced.
[][] is balanced.
][ is unbalanced.
is balanced.
R
balanced <- function(str){
str <- strsplit(str, "")[[1]]
str <- ifelse(str=='[', 1, -1)
all(cumsum(str) >= 0) && sum(str) == 0
}Alternately, using perl 5.10-compatible regexps,
balanced <- function(str) {
regexpr('^(\\[(?1)*\\])*$', str, perl=TRUE) > -1
}To generate some some examples:
rand.parens <- function(n) paste(sample(c("[","]"),2*n,replace=T),collapse="")
as.data.frame(within(list(), {
parens <- replicate(10, rand.parens(sample.int(10,size=1)))
balanced <- sapply(parens, balanced)
}))Output:
balanced parens
1 FALSE ][][
2 FALSE [][[]]][[]][]]][[[
3 FALSE ][[][][]][][[]
4 FALSE ][][][][][][][
5 TRUE [[[][]]][[[][][]]]
6 TRUE []
7 FALSE ]][[][[]
8 FALSE []]]][[[]][[[]
9 TRUE [[[[][[][]]]]]
10 TRUE []Racket
#lang racket
(define (generate n)
(list->string (shuffle (append* (make-list n '(#\[ #\]))))))
(define (balanced? str)
(let loop ([l (string->list str)] [n 0])
(or (null? l)
(if (eq? #\[ (car l))
(loop (cdr l) (add1 n))
(and (> n 0) (loop (cdr l) (sub1 n)))))))
(define (try n)
(define s (generate n))
(printf "~a => ~a\n" s (if (balanced? s) "OK" "NOT OK")))
(for ([n 10]) (try n))Raku
(formerly Perl 6) There's More Than One Way To Do It.
Depth counter
sub balanced($s) {
my $l = 0;
for $s.comb {
when "]" {
--$l;
return False if $l < 0;
}
when "[" {
++$l;
}
}
return $l == 0;
}
my $n = prompt "Number of brackets";
my $s = (<[ ]> xx $n).flat.pick(*).join;
say "$s {balanced($s) ?? "is" !! "is not"} well-balanced"FP oriented
Here's a more idiomatic solution using a hyperoperator to compare all the characters to a backslash (which is between the brackets in ASCII), a triangle reduction to return the running sum, a given to make that list the topic, and then a topicalized junction and a topicalized subscript to test the criteria for balance.
sub balanced($s) {
.none < 0 and .[*-1] == 0
given ([\+] '\\' «leg« $s.comb).cache;
}
my $n = prompt "Number of bracket pairs: ";
my $s = <[ ]>.roll($n*2).join;
say "$s { balanced($s) ?? "is" !! "is not" } well-balanced"String munging
Of course, a Perl 5 programmer might just remove as many inner balanced pairs as possible and then see what's left.
sub balanced($_ is copy) {
Nil while s:g/'[]'//;
$_ eq '';
}
my $n = prompt "Number of bracket pairs: ";
my $s = <[ ]>.roll($n*2).join;
say "$s is", ' not' x not balanced($s), " well-balanced";Parsing with a grammar
grammar BalBrack { token TOP { '[' <TOP>* ']' } }
my $n = prompt "Number of bracket pairs: ";
my $s = ('[' xx $n, ']' xx $n).flat.pick(*).join;
say "$s { BalBrack.parse($s) ?? "is" !! "is not" } well-balanced";Red
; Functional code
balanced-brackets: [#"[" any balanced-brackets #"]"]
rule: [any balanced-brackets end]
balanced?: func [str][parse str rule]
; Tests
tests: [
good: ["" "[]" "[][]" "[[]]" "[[][]]" "[[[[[]]][][[]]]]"]
bad: ["[" "]" "][" "[[]" "[]]" "[]][[]" "[[[[[[]]]]]]]"]
]
foreach str tests/good [
if not balanced? str [print [mold str "failed!"]]
]
foreach str tests/bad [
if balanced? str [print [mold str "failed!"]]
]
repeat i 10 [
str: random copy/part "[][][][][][][][][][]" i * 2
print [mold str "is" either balanced? str ["balanced"]["unbalanced"]]
]REXX
with 40 examples
/*REXX program checks for balanced brackets [ ] ─── some fixed, others random.*/
parse arg seed . /*obtain optional argument from the CL.*/
if datatype(seed,'W') then call random ,,seed /*if specified, then use as RANDOM seed*/
@.=0; yesNo.0= right('not OK', 50) /*for bad expressions, indent 50 spaces*/
yesNo.1= 'OK' /* [↓] the 14 "fixed" ][ expressions*/
q= ; call checkBal q; say yesNo.result '«null»'
q= '[][][][[]]' ; call checkBal q; say yesNo.result q
q= '[][][][[]]][' ; call checkBal q; say yesNo.result q
q= '[' ; call checkBal q; say yesNo.result q
q= ']' ; call checkBal q; say yesNo.result q
q= '[]' ; call checkBal q; say yesNo.result q
q= '][' ; call checkBal q; say yesNo.result q
q= '][][' ; call checkBal q; say yesNo.result q
q= '[[]]' ; call checkBal q; say yesNo.result q
q= '[[[[[[[]]]]]]]' ; call checkBal q; say yesNo.result q
q= '[[[[[]]]][]' ; call checkBal q; say yesNo.result q
q= '[][]' ; call checkBal q; say yesNo.result q
q= '[]][[]' ; call checkBal q; say yesNo.result q
q= ']]][[[[]' ; call checkBal q; say yesNo.result q
#=0 /*# additional random expressions*/
do j=1 until #==26 /*gen 26 unique bracket strings. */
q=translate( rand( random(1,10) ), '][', 10) /*generate random bracket string.*/
call checkBal q; if result==-1 then iterate /*skip if duplicated expression. */
say yesNo.result q /*display the result to console. */
#=#+1 /*bump the expression counter. */
end /*j*/ /* [↑] generate 26 random "Q" strings.*/
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
?: ?=random(0,1); return ? || \? /*REXX BIF*/
rand: $=copies(?()?(),arg(1)); _=random(2,length($)); return left($,_-1)substr($,_)
/*──────────────────────────────────────────────────────────────────────────────────────*/
checkBal: procedure expose @.; parse arg y /*obtain the "bracket" expression. */
if @.y then return -1 /*Done this expression before? Skip it*/
@.y=1 /*indicate expression was processed. */
!=0; do j=1 for length(y); _=substr(y,j,1) /*get a character.*/
if _=='[' then !=!+1 /*bump the nest #.*/
else do; !=!-1; if !<0 then return 0; end
end /*j*/
return !==0 /* [↑] "!" is the nested ][ counter.*/output using the (some internal, others random) expressions:
OK «null»
OK [][][][[]]
not OK [][][][[]]][
not OK [
not OK ]
OK []
not OK ][
not OK ][][
OK [[]]
OK [[[[[[[]]]]]]]
not OK [[[[[]]]][]
OK [][]
not OK []][[]
not OK ]]][[[[]
not OK []][
OK [][][][][][][][][][][][]
not OK []][[]][[]][[]][[]][[]][[]][[]][
not OK []][[]][[]][[]][[]][[]][[]][[]][[]][[]][
not OK ][[]][[]
not OK ][][][][][][][][][][][][][][][][
not OK ][[]][[]][[]
not OK []][[]][
not OK ][][][][][][
OK [][][][][][]
OK [][][][][][][][][][][][][][]
OK [][][][][][][][][][][][][][][][][][][][]
not OK []][[]][[]][[]][
not OK ][[]
not OK []][[]][[]][[]][[]][[]][[]][
not OK ][[]][[]][[]][[]][[]
not OK []][[]][[]][[]][[]][[]][
OK [][][][][][][][][][][][][][][][]
not OK ][[]][[]][[]][[]][[]][[]][[]][[]
not OK ][][][][][][][][][][][][
not OK ][[]][[]][[]][[]][[]][[]][[]
not OK ][[]][[]][[]][[]][[]][[]][[]][[]][[]][[]
not OK ][][][][][][][][][][][][][][][][][][
OK [][][][][][][][]
not OK ][[]][[]][[]][[]
not OK ][][][][][][][][][][][][][][][][][][][][
with examples + 30 permutations
/*REXX program to check for balanced brackets [] **********************
* test strings and random string generation copied from Version 1
* the rest restructured (shortened) to some extent
* and output made reproducible (random with a seed)
* 10.07.2012 Walter Pachl
**********************************************************************/
yesno.0 = 'unbalanced'
yesno.1 = ' balanced'
done.=0 /* memory what's been done */
n=0 /* number of tests */
Call testbal '[][][][[]]' /* first some user written tests */
Call testbal '[][][][[]]]['
Call testbal '['
Call testbal ']'
Call testbal '[]'
Call testbal ']['
Call testbal '][]['
Call testbal '[[]]'
Call testbal '[[[[[[[]]]]]]]'
Call testbal '[[[[[]]]][]'
Call testbal '[][]'
Call testbal '[]][[]'
Call testbal ']]][[[[]'
Call testbal ']'
Call testbal '['
/* then some random generated ones */
Call random 1,2,12345 /* call random with a seed */
/* makes test reproducible */
do Until n=30 /* up to 30 tests */
s=rand(random(1,8)) /* a 01 etc. string of length 4-32 */
q=translate(s,'[]',01) /* turn digits into brackets */
if done.q then /* string was already here */
iterate /* don't test again */
call testbal q /* test balance */
End
exit
testbal: /* test the given string and show result */
n=n+1 /* number of tests */
Parse Arg q /* get string to be tested */
done.q=1 /* mark as done */
call checkBal q /* test balance */
lq=format(length(q),2)
say right(n,2) lq yesno.result q/* show result and string */
Return
/*-----------------------------------PAND subroutine-----------------*/
pand: p=random(0,1); return p || \p
/*-----------------------------------RAND subroutine-----------------*/
rand: pp=pand(); pp=pand()pp; pp=copies(pp,arg(1))
i=random(2,length(pp)); pp=left(pp,i-1)substr(pp,i)
return pp
checkBal: procedure /*check for balanced brackets () */
Parse arg y
nest=0;
do While y<>''
Parse Var y c +1 y /*pick off one character at a time */
if c='[' then /* opening bracket */
nest=nest+1 /* increment nesting */
else do /* closing bracket */
if nest=0 then /* not allowed */
return 0; /* no success */
nest=nest-1 /* decrement nesting */
end
end
return nest=0 /* nest=0 -> balanced */- Output:
1 10 balanced [][][][[]] 2 12 unbalanced [][][][[]]][ 3 1 unbalanced [ 4 1 unbalanced ] 5 2 balanced [] 6 2 unbalanced ][ 7 4 unbalanced ][][ 8 4 balanced [[]] 9 14 balanced [[[[[[[]]]]]]] 10 11 unbalanced [[[[[]]]][] 11 4 balanced [][] 12 6 unbalanced []][[] 13 8 unbalanced ]]][[[[] 14 1 unbalanced ] 15 1 unbalanced [ 16 20 unbalanced ][][][][][][][][][][ 17 24 unbalanced ][][][][][][][][][][][][ 18 20 unbalanced []][[]][[]][[]][[]][ 19 20 balanced [][][][][][][][][][] 20 24 balanced [][][][][][][][][][][][] 21 24 unbalanced []][[]][[]][[]][[]][[]][ 22 12 balanced [][][][][][] 23 32 balanced [][][][][][][][][][][][][][][][] 24 8 unbalanced []][[]][ 25 32 unbalanced ][[]][[]][[]][[]][[]][[]][[]][[] 26 4 unbalanced ][[] 27 28 unbalanced ][[]][[]][[]][[]][[]][[]][[] 28 32 unbalanced ][][][][][][][][][][][][][][][][ 29 28 unbalanced []][[]][[]][[]][[]][[]][[]][ 30 4 unbalanced []][
with over 125,000 permutations
This REXX version generates over one hundred thousand unique permutations of strings that contain an equal
amount of left [ and right ] brackets.
All possible strings of twenty or less characters (legal bracket expressions) are generated.
This eliminates the possibility of missing a particular character string permutation that may not be generated
via a random generator.
Use is made of the countstr function (which is a BIF for newer REXX interpreters), but a RYO version is
included here for older REXXes that don't contain that BIF (Built In Function).
Naturally, each of the one hundred thousand character strings aren't displayed (for balanced/not-balanced),
but a count is displayed, as anyone can generate the same strings in other languages and compare results.
/*REXX program checks for around 125,000 generated balanced brackets expressions [ ] */
bals=0
#=0; do j=1 until L>20 /*generate lots of bracket permutations*/
q=translate( strip( x2b( d2x(j) ), 'L', 0), "][", 01) /*convert ──► ][*/
L=length(q)
if countStr(']', q) \== countstr('[', q) then iterate /*not compliant?*/
#=#+1 /*bump legal Q's*/
!=0; do k=1 for L; parse var q ? 2 q
if ?=='[' then !=!+1
else do; !=!-1; if !<0 then iterate j; end
end /*k*/
if !==0 then bals=bals+1
end /*j*/ /*done all 20─character possibilities? */
say # " expressions were checked, " bals ' were balanced, ' ,
#-bals " were unbalanced."
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
countStr: procedure; parse arg n,h,s; if s=='' then s=1; w=length(n)
do r=0 until _==0; _=pos(n,h,s); s=_+w; end; return routput when using the default input:
125476 expressions were checked, 23713 were balanced, 101763 were unbalanced.
Ring
nr = 0
while nr < 10
nr += 1
test=generate(random(9)+1)
see "bracket string " + test + " is " + valid(test) + nl
end
func generate n
l = 0 r = 0 output = ""
while l<n and r<n
switch random(2)
on 1 l+=1 output+="["
on 2 r+=1 output+="]"
off
end
if l=n output+=copy("]",n-r) else output+=copy("]",n-l) ok
return output
func valid q
count = 0
if len(q)=0 return "ok." ok
for x=1 to len(q)
if substr(q,x,1)="[" count+=1 else count-=1 ok
if count<0 return "not ok." ok
next
return "ok."Output:
bracket string ]][[][[[[]]] is not ok. bracket string [[[]]] is ok. bracket string ]][[[[[[[]]]]] is not ok. bracket string [][[[][[][]]][]] is ok. bracket string [[]][][[][[][[]]]] is ok. bracket string ]] is not ok. bracket string [[[]]] is ok. bracket string [][[]] is ok. bracket string [[]] is ok. bracket string ]]]][]]]]]]]]] is not ok.
RPL
« (1,1) * → count
« ""
WHILE count ABS REPEAT
IF RAND .5 < THEN
IF count RE THEN 'count' 1 STO- "[" + END
ELSE
IF count IM THEN 'count' (0,1) STO- "]" + END
END
END
» » 'BKT→' STO
« DUP DUP SIZE → brackets length
« 0
1 length FOR j
"][" brackets j DUP SUB POS 2 * 3 - +
IF DUP 0 < THEN length 'j' STO END
NEXT
"un" "" IFTE "balanced" + →TAG
» » 'BALBKT?' STO
20 BKT→ BALBKT?
- Output:
1: unbalanced: "]]]]]]]][][]][][][]]]][[][[[][[[[[[[][[["
Ruby
re = /\A # beginning of string
(?<bb> # begin capture group <bb>
\[ # literal [
\g<bb>* # zero or more <bb>
\] # literal ]
)* # end group, zero or more such groups
\z/x # end of string
10.times do |i|
s = (%w{[ ]} * i).shuffle.join
puts (s =~ re ? " OK: " : "bad: ") + s
end
["[[]", "[]]", "a[ letters[-1] ].xyz[0]"].each do |s|
t = s.gsub(/[^\[\]]/, "")
puts (t =~ re ? " OK: " : "bad: ") + s
endOne output:
OK: OK: [] bad: []][ OK: [[][]] bad: []]][][[ bad: ][]][[[[]] bad: []]][[]][[[] bad: ][[][]][][[]][ OK: [][[][[[]][]][]] bad: []][][]][[[[[][]]] bad: [[] bad: []] OK: a[ letters[-1] ].xyz[0]
Run BASIC
dim brk$(10)
brk$(1) = "[[[][]]]"
brk$(2) = "[[[]][[[][[][]]]]]"
brk$(3) = "][][]][["
brk$(4) = "[][][]"
brk$(5) = "[][]][]][[]]][[["
brk$(6) = "]][[[[]]]][]]][[[["
brk$(7) = "[[][[[]]][]]"
brk$(8) = "[]][][][[[]]"
brk$(9) = "][]][["
brk$(10) = "[]][][][[]"
for i = 0 to 10
b$ = brk$(i)
while instr(b$,"[]") <> 0
x = instr(b$,"[]")
if x > 0 then b$ = left$(b$,x - 1) + mid$(b$,x + 2)
wend
if trim$(b$) = "" then print " OK "; else print "Not OK ";
print brk$(i)
next iOne output:
OK
OK [[[][]]]
OK [[[]][[[][[][]]]]]
Not OK ][][]][[
OK [][][]
Not OK [][]][]][[]]][[[
Not OK ]][[[[]]]][]]][[[[
OK [[][[[]]][]]
Not OK []][][][[[]]
Not OK ][]][[
Not OK []][][][[]
Rust
extern crate rand;
trait Balanced {
/// Returns true if the brackets are balanced
fn is_balanced(&self) -> bool;
}
impl<'a> Balanced for str {
fn is_balanced(&self) -> bool {
let mut count = 0;
for bracket in self.chars() {
let change = match bracket {
'[' => 1,
']' => -1,
_ => panic!("Strings should only contain brackets")
};
count += change;
if count < 0 { return false; }
}
count == 0
}
}
/// Generates random brackets
fn generate_brackets(num: usize) -> String {
use rand::random;
(0..num).map(|_| if random() { '[' } else { ']' }).collect()
}
fn main() {
for i in (0..10) {
let brackets = generate_brackets(i);
println!("{} {}", brackets, brackets.is_balanced())
}
}Output:
true [ false ]] false ][] false [[[[ false ]][[[ false [][[]] true []]][[] false [[[[[[][ false ][[[[][]] false
Scala
If you are new to Scala you might want to jump to Version 2.
Scala Version 1
import scala.collection.mutable.ListBuffer
import scala.util.Random
object BalancedBrackets extends App {
val random = new Random()
def generateRandom: List[String] = {
import scala.util.Random._
val shuffleIt: Int => String = i => shuffle(("["*i+"]"*i).toList).foldLeft("")(_+_)
(1 to 20).map(i=>(random.nextDouble*100).toInt).filter(_>2).map(shuffleIt(_)).toList
}
def generate(n: Int): List[String] = {
val base = "["*n+"]"*n
var lb = ListBuffer[String]()
base.permutations.foreach(s=>lb+=s)
lb.toList.sorted
}
def checkBalance(brackets: String):Boolean = {
def balI(brackets: String, depth: Int):Boolean = {
if (brackets == "") depth == 0
else brackets(0) match {
case '[' => ((brackets.size > 1) && balI(brackets.substring(1), depth + 1))
case ']' => (depth > 0) && ((brackets.size == 1) || balI(brackets.substring(1), depth -1))
case _ => false
}
}
balI(brackets, 0)
}
println("arbitrary random order:")
generateRandom.map(s=>Pair(s,checkBalance(s))).foreach(p=>println((if(p._2) "balanced: " else "unbalanced: ")+p._1))
println("\n"+"check all permutations of given length:")
(1 to 5).map(generate(_)).flatten.map(s=>Pair(s,checkBalance(s))).foreach(p=>println((if(p._2) "balanced: " else "unbalanced: ")+p._1))
}arbitrary random order: unbalanced: ][[[]][][[]]][][]]]][[]]]][[][]][[]]][[][]]][[[]][[][[]]][[]]]]][][]]][[][]]]][[][[][[][[][][][[][]][][[][[[][]]][[]]]][][]][[][]]][[][][[[][[[][[[[[][[]][[[[[[[][]][[]][]]][[[]][[][[]][][]] unbalanced: [[][][[[[][]]][][[][]][][[[]]]][]][]][]][][]][[]]]][[][[[]][][[][[[[[][[][][[]]][]]] unbalanced: [[]][][][[[[][][][[[[[[[][[[]]][[[[]]][[]]]][]][]]]][]][]]][]]]]][][][[]]][]][]][]]][[]][][]][]][[[[[[][[[[][[[]][[][[[][[]][]][[[][[][]]][]]][[[[][][[[]][][][[[[]]][]]][][]]]][][][][]][ unbalanced: []]][]][[]]][]][]]]][]]]][]]]][][[][[][[[[][][[[[[[[[][[[] unbalanced: [][[[]]][]]][[]]]]]][[[[[][][][][]]][[]]]]]][][[[]][[[[][][[][]][]][[[[][[[[[[[[][]]]]]][]][][[][]]][[ unbalanced: []][[][[]] unbalanced: []][[[[][]][][[]][][[[]]]][[]][[[[[][][[[[][]]]]][]][]]][[[]][[[[[]]][[]][][[][][][]]][]]]][][][[[[]]][[]][][]][[]]]][[[[][[][][[[]][[]]]]]]][[]][[[][[][]][][[]][[]][]]][][[][][][[[[]][]][][ unbalanced: ][][[]][[[][[]][[][[[]]]]]][ unbalanced: [][]][][]][[ unbalanced: [[[][[]]]][][][][][][][]]]][[][][]][]]]]][[]]][][[]][]]][[][[][[][]][[]]]]][[[[][[][[]]][]]][][]][]]][][[[[]]][][[[][[[[]]][][]][][[[[[][][[][[][[][[][[[] unbalanced: ][][[]][]]]][[][[][[][]]]][[[[ balanced: [[[]]][[[[]][]]][][[[]]][][] unbalanced: [[[]][]]]][][[[[[[[[[[[[][[]][[[[[[]][]]]][[]]]][]]]]][]]]]][[][[][][][[][[]][]]][[][[]][[[][]]]][]]]]][]][[[[ unbalanced: [[]][[]][[[[][][][][]]]][]]][][[][]]]][[[[ unbalanced: [][[]]][]]][[]]][[[]]][[][[]]]]][[[][]][[[[[[[[][[]]][][][[[]]][[][[][][]][]]][][]][]][]]][]][]][[[[[][[][[] unbalanced: ][][[][][[[[][][[][[[][]]]]]][][][[][][[][[][[]]][[[[]]]][][[][[]][]]][[[][[[][][[[][]][[]]]][[][[]]]]]][[[][]][[[]]]]]] unbalanced: ][[][[][][]][]][][[][][]][][][[[[][]]][[]]][[] unbalanced: ]][][[]]]]][][[[][][]][[[[]][]]][]][[[]]][]]][[[[][[]]]][]][]][]][][[][[[]]][][][[][][[[[]][]]][]][[[[][]]]][][[][[][[[[[][[][]][[]][]]][][[]][]]][[[[][]][][]][[][]][[][[[[][ check all permutations of given length: balanced: [] unbalanced: ][ balanced: [[]] balanced: [][] unbalanced: []][ unbalanced: ][[] unbalanced: ][][ unbalanced: ]][[ balanced: [[[]]] balanced: [[][]] balanced: [[]][] unbalanced: [[]]][ balanced: [][[]] balanced: [][][] unbalanced: [][]][ unbalanced: []][[] unbalanced: []][][ unbalanced: []]][[ unbalanced: ][[[]] unbalanced: ][[][] unbalanced: ][[]][ unbalanced: ][][[] unbalanced: ][][][ unbalanced: ][]][[ unbalanced: ]][[[] unbalanced: ]][[][ unbalanced: ]][][[ unbalanced: ]]][[[ balanced: [[[[]]]] balanced: [[[][]]] balanced: [[[]][]] balanced: [[[]]][] unbalanced: [[[]]]][ balanced: [[][[]]] balanced: [[][][]] balanced: [[][]][] unbalanced: [[][]]][ balanced: [[]][[]] balanced: [[]][][] unbalanced: [[]][]][ unbalanced: [[]]][[] unbalanced: [[]]][][ unbalanced: [[]]]][[ balanced: [][[[]]] balanced: [][[][]] balanced: [][[]][] unbalanced: [][[]]][ balanced: [][][[]] balanced: [][][][] unbalanced: [][][]][ unbalanced: [][]][[] unbalanced: [][]][][ unbalanced: [][]]][[ unbalanced: []][[[]] unbalanced: []][[][] unbalanced: []][[]][ unbalanced: []][][[] unbalanced: []][][][ unbalanced: []][]][[ unbalanced: []]][[[] unbalanced: []]][[][ unbalanced: []]][][[ unbalanced: []]]][[[ unbalanced: ][[[[]]] unbalanced: ][[[][]] unbalanced: ][[[]][] unbalanced: ][[[]]][ unbalanced: ][[][[]] unbalanced: ][[][][] unbalanced: ][[][]][ unbalanced: ][[]][[] unbalanced: ][[]][][ unbalanced: ][[]]][[ unbalanced: ][][[[]] unbalanced: ][][[][] unbalanced: ][][[]][ unbalanced: ][][][[] unbalanced: ][][][][ unbalanced: ][][]][[ unbalanced: ][]][[[] unbalanced: ][]][[][ unbalanced: ][]][][[ unbalanced: ][]]][[[ unbalanced: ]][[[[]] unbalanced: ]][[[][] unbalanced: ]][[[]][ unbalanced: ]][[][[] unbalanced: ]][[][][ unbalanced: ]][[]][[ unbalanced: ]][][[[] unbalanced: ]][][[][ unbalanced: ]][][][[ unbalanced: ]][]][[[ unbalanced: ]]][[[[] unbalanced: ]]][[[][ unbalanced: ]]][[][[ unbalanced: ]]][][[[ unbalanced: ]]]][[[[ balanced: [[[[[]]]]] balanced: [[[[][]]]] balanced: [[[[]][]]] balanced: [[[[]]][]] balanced: [[[[]]]][] unbalanced: [[[[]]]]][ balanced: [[[][[]]]] balanced: [[[][][]]] balanced: [[[][]][]] balanced: [[[][]]][] unbalanced: [[[][]]]][ balanced: [[[]][[]]] balanced: [[[]][][]] balanced: [[[]][]][] unbalanced: [[[]][]]][ balanced: [[[]]][[]] balanced: [[[]]][][] unbalanced: [[[]]][]][ unbalanced: [[[]]]][[] unbalanced: [[[]]]][][ unbalanced: [[[]]]]][[ balanced: [[][[[]]]] balanced: [[][[][]]] balanced: [[][[]][]] balanced: [[][[]]][] unbalanced: [[][[]]]][ balanced: [[][][[]]] balanced: [[][][][]] balanced: [[][][]][] unbalanced: [[][][]]][ balanced: [[][]][[]] balanced: [[][]][][] unbalanced: [[][]][]][ unbalanced: [[][]]][[] unbalanced: [[][]]][][ unbalanced: [[][]]]][[ balanced: [[]][[[]]] balanced: [[]][[][]] balanced: [[]][[]][] unbalanced: [[]][[]]][ balanced: [[]][][[]] balanced: [[]][][][] unbalanced: [[]][][]][ unbalanced: [[]][]][[] unbalanced: [[]][]][][ unbalanced: [[]][]]][[ unbalanced: [[]]][[[]] unbalanced: [[]]][[][] unbalanced: [[]]][[]][ unbalanced: [[]]][][[] unbalanced: [[]]][][][ unbalanced: [[]]][]][[ unbalanced: [[]]]][[[] unbalanced: [[]]]][[][ unbalanced: [[]]]][][[ unbalanced: [[]]]]][[[ balanced: [][[[[]]]] balanced: [][[[][]]] balanced: [][[[]][]] balanced: [][[[]]][] unbalanced: [][[[]]]][ balanced: [][[][[]]] balanced: [][[][][]] balanced: [][[][]][] unbalanced: [][[][]]][ balanced: [][[]][[]] balanced: [][[]][][] unbalanced: [][[]][]][ unbalanced: [][[]]][[] unbalanced: [][[]]][][ unbalanced: [][[]]]][[ balanced: [][][[[]]] balanced: [][][[][]] balanced: [][][[]][] unbalanced: [][][[]]][ balanced: [][][][[]] balanced: [][][][][] unbalanced: [][][][]][ unbalanced: [][][]][[] unbalanced: [][][]][][ unbalanced: [][][]]][[ unbalanced: [][]][[[]] unbalanced: [][]][[][] unbalanced: [][]][[]][ unbalanced: [][]][][[] unbalanced: [][]][][][ unbalanced: [][]][]][[ unbalanced: [][]]][[[] unbalanced: [][]]][[][ unbalanced: [][]]][][[ unbalanced: [][]]]][[[ unbalanced: []][[[[]]] unbalanced: []][[[][]] unbalanced: []][[[]][] unbalanced: []][[[]]][ unbalanced: []][[][[]] unbalanced: []][[][][] unbalanced: []][[][]][ unbalanced: []][[]][[] unbalanced: []][[]][][ unbalanced: []][[]]][[ unbalanced: []][][[[]] unbalanced: []][][[][] unbalanced: []][][[]][ unbalanced: []][][][[] unbalanced: []][][][][ unbalanced: []][][]][[ unbalanced: []][]][[[] unbalanced: []][]][[][ unbalanced: []][]][][[ unbalanced: []][]]][[[ unbalanced: []]][[[[]] unbalanced: []]][[[][] unbalanced: []]][[[]][ unbalanced: []]][[][[] unbalanced: []]][[][][ unbalanced: []]][[]][[ unbalanced: []]][][[[] unbalanced: []]][][[][ unbalanced: []]][][][[ unbalanced: []]][]][[[ unbalanced: []]]][[[[] unbalanced: []]]][[[][ unbalanced: []]]][[][[ unbalanced: []]]][][[[ unbalanced: []]]]][[[[ unbalanced: ][[[[[]]]] unbalanced: ][[[[][]]] unbalanced: ][[[[]][]] unbalanced: ][[[[]]][] unbalanced: ][[[[]]]][ unbalanced: ][[[][[]]] unbalanced: ][[[][][]] unbalanced: ][[[][]][] unbalanced: ][[[][]]][ unbalanced: ][[[]][[]] unbalanced: ][[[]][][] unbalanced: ][[[]][]][ unbalanced: ][[[]]][[] unbalanced: ][[[]]][][ unbalanced: ][[[]]]][[ unbalanced: ][[][[[]]] unbalanced: ][[][[][]] unbalanced: ][[][[]][] unbalanced: ][[][[]]][ unbalanced: ][[][][[]] unbalanced: ][[][][][] unbalanced: ][[][][]][ unbalanced: ][[][]][[] unbalanced: ][[][]][][ unbalanced: ][[][]]][[ unbalanced: ][[]][[[]] unbalanced: ][[]][[][] unbalanced: ][[]][[]][ unbalanced: ][[]][][[] unbalanced: ][[]][][][ unbalanced: ][[]][]][[ unbalanced: ][[]]][[[] unbalanced: ][[]]][[][ unbalanced: ][[]]][][[ unbalanced: ][[]]]][[[ unbalanced: ][][[[[]]] unbalanced: ][][[[][]] unbalanced: ][][[[]][] unbalanced: ][][[[]]][ unbalanced: ][][[][[]] unbalanced: ][][[][][] unbalanced: ][][[][]][ unbalanced: ][][[]][[] unbalanced: ][][[]][][ unbalanced: ][][[]]][[ unbalanced: ][][][[[]] unbalanced: ][][][[][] unbalanced: ][][][[]][ unbalanced: ][][][][[] unbalanced: ][][][][][ unbalanced: ][][][]][[ unbalanced: ][][]][[[] unbalanced: ][][]][[][ unbalanced: ][][]][][[ unbalanced: ][][]]][[[ unbalanced: ][]][[[[]] unbalanced: ][]][[[][] unbalanced: ][]][[[]][ unbalanced: ][]][[][[] unbalanced: ][]][[][][ unbalanced: ][]][[]][[ unbalanced: ][]][][[[] unbalanced: ][]][][[][ unbalanced: ][]][][][[ unbalanced: ][]][]][[[ unbalanced: ][]]][[[[] unbalanced: ][]]][[[][ unbalanced: ][]]][[][[ unbalanced: ][]]][][[[ unbalanced: ][]]]][[[[ unbalanced: ]][[[[[]]] unbalanced: ]][[[[][]] unbalanced: ]][[[[]][] unbalanced: ]][[[[]]][ unbalanced: ]][[[][[]] unbalanced: ]][[[][][] unbalanced: ]][[[][]][ unbalanced: ]][[[]][[] unbalanced: ]][[[]][][ unbalanced: ]][[[]]][[ unbalanced: ]][[][[[]] unbalanced: ]][[][[][] unbalanced: ]][[][[]][ unbalanced: ]][[][][[] unbalanced: ]][[][][][ unbalanced: ]][[][]][[ unbalanced: ]][[]][[[] unbalanced: ]][[]][[][ unbalanced: ]][[]][][[ unbalanced: ]][[]]][[[ unbalanced: ]][][[[[]] unbalanced: ]][][[[][] unbalanced: ]][][[[]][ unbalanced: ]][][[][[] unbalanced: ]][][[][][ unbalanced: ]][][[]][[ unbalanced: ]][][][[[] unbalanced: ]][][][[][ unbalanced: ]][][][][[ unbalanced: ]][][]][[[ unbalanced: ]][]][[[[] unbalanced: ]][]][[[][ unbalanced: ]][]][[][[ unbalanced: ]][]][][[[ unbalanced: ]][]]][[[[ unbalanced: ]]][[[[[]] unbalanced: ]]][[[[][] unbalanced: ]]][[[[]][ unbalanced: ]]][[[][[] unbalanced: ]]][[[][][ unbalanced: ]]][[[]][[ unbalanced: ]]][[][[[] unbalanced: ]]][[][[][ unbalanced: ]]][[][][[ unbalanced: ]]][[]][[[ unbalanced: ]]][][[[[] unbalanced: ]]][][[[][ unbalanced: ]]][][[][[ unbalanced: ]]][][][[[ unbalanced: ]]][]][[[[ unbalanced: ]]]][[[[[] unbalanced: ]]]][[[[][ unbalanced: ]]]][[[][[ unbalanced: ]]]][[][[[ unbalanced: ]]]][][[[[ unbalanced: ]]]]][[[[[
Scala Version 2
import scala.util.Random.shuffle
object BalancedBracketsApp extends App {
for (length <- 0 until 10) {
val str = randomBrackets(length)
if (is_balanced(str))
println(s"$str - ok")
else
println(s"$str - NOT ok")
}
def randomBrackets(length: Int): String =
shuffle(("[]" * length).toSeq).mkString
def isBalanced(bracketString: String): Boolean = {
var balance = 0
for (char <- bracketString) {
char match {
case '[' => balance += 1
case ']' => balance -= 1
}
if (balance < 0) return false;
}
balance == 0
}
}Alternate implementation of "isBalanced" using tail-recursion instead of var and return:
import scala.util.Random.shuffle
import scala.annotation.tailrec
// ...
def isBalanced(str: String): Boolean = isBalanced(str.toList, balance = 0)
@tailrec
def isBalanced(str: List[Char], balance: Int = 0): Boolean =
str match {
case _ if (balance < 0) => false
case Nil => balance == 0
case char :: rest =>
val newBalance = char match {
case '[' => balance + 1
case ']' => balance -1
}
isBalanced(rest, newBalance)
}Slightly modified implementation of "isBalanced" using tail-recursion
@scala.annotation.tailrec
final def isBalanced(
str: List[Char],
// accumulator|indicator|flag
balance: Int = 0,
options_Map: Map[Char, Int] = Map(('[' -> 1), (']' -> -1))
): Boolean = if (balance < 0) {
// base case
false
} else {
if (str.isEmpty){
// base case
balance == 0
} else {
// recursive step
isBalanced(str.tail, balance + options_Map(str.head))
}
}Sample output:
- ok [ - NOT ok [] - ok [][ - NOT ok ][][ - NOT ok [][][ - NOT ok [][][] - ok [[[]][] - NOT ok [[][][]] - ok [[[][]][] - NOT ok
Scheme
(define (balanced-brackets string)
(define (b chars sum)
(cond ((< sum 0)
#f)
((and (null? chars) (= 0 sum))
#t)
((null? chars)
#f)
((char=? #\[ (car chars))
(b (cdr chars) (+ sum 1)))
((char=? #\] (car chars))
(b (cdr chars) (- sum 1)))
(else
(#f)))
(b (string->list string) 0))
(balanced-brackets "")
(balanced-brackets "[]")
(balanced-brackets "[][]")
(balanced-brackets "[[][]]")
(balanced-brackets "][")
(balanced-brackets "][][")
(balanced-brackets "[]][[]")Scilab
function varargout=isbb(s)
st=strsplit(s);
t=cumsum((st=='[')-(st==']'));
balanced=and(t>=0) & t(length(t))==0;
varargout=list(balanced)
endfunction- Output:
The following code was used to generate random strings of length 5, 16, and 22 chars. It also displays the generated string, and the output (true of false) of isbb().
for j=[5 16 22]
s=[];
for i=1:j
p=rand();
if p>0.5 then
s=s+"[";
else
s=s+"]";
end
end
disp(s);
x=isbb(s);
disp(x);
endConsole output:
][]][ F [[[[][[[][]]]]]] T ][[][]]]][]][[]][][]]] F
Seed7
$ include "seed7_05.s7i";
const func string: generateBrackets (in integer: count) is func
result
var string: stri is "";
local
var integer: index is 0;
var integer: pos is 0;
var char: ch is ' ';
begin
stri := "[" mult count & "]" mult count;
for index range 1 to length(stri) do
pos := rand(1, length(stri));
ch := stri[index];
stri @:= [index] stri[pos];
stri @:= [pos] ch;
end for;
end func;
const func boolean: checkBrackets (in string: test) is func
result
var boolean: okay is TRUE;
local
var char: ch is ' ';
var integer: open is 0;
begin
for ch range test do
if ch = '[' then
incr(open);
elsif ch = ']' then
if open = 0 then
okay := FALSE;
else
decr(open);
end if;
end if;
end for;
okay := open = 0;
end func;
const proc: main is func
local
var integer: n is 0;
var integer: count is 0;
var string: stri is "";
begin
for n range 0 to 4 do
for count range 1 to 3 do
stri := generateBrackets(n);
writeln(stri <& ": " <& checkBrackets(stri));
end for;
end for;
end func;Output:
: TRUE : TRUE : TRUE []: TRUE ][: FALSE ][: FALSE ][[]: FALSE [[]]: TRUE [[]]: TRUE [][][]: TRUE [[][]]: TRUE []]][[: FALSE [][][]][: FALSE [][][][]: TRUE ]][][[][: FALSE
SETL
program balanced_brackets;
setrandom(0);
loop for length in [1..10] do
s := generate length;
print(balanced s, s);
end loop;
op generate(n);
s := "["*n + "]"*n;
loop for i in [n*2, n*2-1..2] do
j := 1 + random(i - 1);
[s(i), s(j)] := [s(j), s(i)];
end loop;
return s;
end op;
op balanced(s);
depth := 0;
loop for c in s do
case c of
("["):
depth +:= 1;
("]"):
depth -:= 1;
if depth<0 then return false; end if;
end case;
end loop;
return depth = 0;
end op;
end program;- Output:
#F ][ #F ]][[ #T [[]][] #F [[]]][][ #F ][[][][]][ #F ]][]]]][[[[[ #F ]]][[]]][[[[[] #T [[][][[][[]][]]] #F []][[]]]][][][[][[ #F []][]]][]][][[[][[][
Sidef
func balanced (str) {
var depth = 0
str.each { |c|
if(c=='['){ ++depth }
elsif(c==']'){ --depth < 0 && return false }
}
return !depth
}
for str [']','[','[[]','][]','[[]]','[[]]]][][]]','x[ y [ [] z ]][ 1 ][]abcd'] {
printf("%sbalanced\t: %s\n", balanced(str) ? "" : "NOT ", str)
}- Output:
NOT balanced : ] NOT balanced : [ NOT balanced : [[] NOT balanced : ][] balanced : [[]] NOT balanced : [[]]]][][]] balanced : x[ y [ [] z ]][ 1 ][]abcd
Simula
BEGIN
INTEGER U;
U := ININT;
BEGIN
TEXT PROCEDURE GENERATE(N); INTEGER N;
BEGIN
INTEGER R;
TEXT T;
T :- NOTEXT;
WHILE N > 0 DO BEGIN
R := RANDINT(1,2,U);
T :- T & (IF R = 1 THEN "[" ELSE "]");
N := N - 1;
END;
GENERATE :- T;
END GENERATE;
BOOLEAN PROCEDURE BALANCED(T); TEXT T;
BEGIN
INTEGER LEVEL;
CHARACTER BRACE;
BOOLEAN DONE;
T.SETPOS(1);
WHILE T.MORE AND NOT DONE DO BEGIN
BRACE := T.GETCHAR;
IF BRACE = '[' THEN LEVEL := LEVEL + 1;
IF BRACE = ']' THEN LEVEL := LEVEL - 1;
IF LEVEL < 0 THEN DONE := TRUE;
END;
BALANCED := LEVEL = 0;
END BALANCED;
INTEGER I,M;
TEXT T;
FOR I := 1 STEP 1 UNTIL 40 DO BEGIN
M := RANDINT(0,10,U);
T :- GENERATE(M);
IF BALANCED(T) THEN OUTTEXT(" ") ELSE OUTTEXT(" NOT");
OUTTEXT(" BALANCED: ");
OUTTEXT(T);
OUTIMAGE;
END;
END;
END- Input:
710
- Output:
NOT BALANCED: [[[[[[][
NOT BALANCED: [[[[]
NOT BALANCED: ][
NOT BALANCED: [][[[[
BALANCED: [][[]]
NOT BALANCED: [[]
NOT BALANCED: ][
NOT BALANCED: ]][[]
NOT BALANCED: []]]
NOT BALANCED: ][]][[]
NOT BALANCED: ]]][
NOT BALANCED: ]][
NOT BALANCED: ][]]]]][]
NOT BALANCED: [[][[[]][[
NOT BALANCED: ]][]][]]
BALANCED:
NOT BALANCED: ][[
NOT BALANCED: []]][[]
NOT BALANCED: ]]]][[]]][
NOT BALANCED: ]]
BALANCED: [[][[[]]]]
NOT BALANCED: ][][]]
BALANCED:
NOT BALANCED: [[[[[]][[]
NOT BALANCED: []][[[][
NOT BALANCED: []]]][][]
NOT BALANCED: ][]][][
NOT BALANCED: []]
NOT BALANCED: ]]][[
NOT BALANCED: [
BALANCED: []
NOT BALANCED: ][]]]
NOT BALANCED: [[[[[[]][
NOT BALANCED: [][[][
NOT BALANCED: ]]
NOT BALANCED: ]][
NOT BALANCED: [[[[[[
NOT BALANCED: ]]]]]
NOT BALANCED: ]][[]
NOT BALANCED: ][][][][
Standard ML
fun isBalanced s = checkBrackets 0 (String.explode s)
and checkBrackets 0 [] = true
| checkBrackets _ [] = false
| checkBrackets ~1 _ = false
| checkBrackets counter (#"["::rest) = checkBrackets (counter + 1) rest
| checkBrackets counter (#"]"::rest) = checkBrackets (counter - 1) rest
| checkBrackets counter (_::rest) = checkBrackets counter restAn example of usage
val () =
List.app print
(List.map
(* Turn `true' and `false' to `OK' and `NOT OK' respectively *)
(fn s => if isBalanced s
then s ^ "\t\tOK\n"
else s ^ "\t\tNOT OK\n"
)
(* A set of strings to test *)
["", "[]", "[][]", "[[][]]", "][", "][][", "[]][[]"]
)Output:
OK [] OK [][] OK [[][]] OK ][ NOT OK ][][ NOT OK []][[] NOT OK
Stata
mata
function random_brackets(n) {
return(invtokens(("[","]")[runiformint(1,2*n,1,2)],""))
}
function is_balanced(s) {
n = strlen(s)
if (n==0) return(1)
a = runningsum(92:-ascii(s))
return(all(a:>=0) & a[n]==0)
}
endTest
: is_balanced("")
1
: is_balanced("[]")
1
: is_balanced("[][]")
1
: is_balanced("[[][]]")
1
: is_balanced("][")
0
: is_balanced("][][")
0
: is_balanced("[]][[]")
Swift
Checks balance function:
import Foundation
func isBal(str: String) -> Bool {
var count = 0
return !str.characters.contains { ($0 == "[" ? ++count : --count) < 0 } && count == 0
}output:
isBal("[[[]]]") // true
isBal("[]][[]") // falseRandom Bracket function:
func randBrack(n: Int) -> String {
var bracks: [Character] = Array(Repeat(count: n, repeatedValue: "["))
for i in UInt32(n+1)...UInt32(n + n) {
bracks.insert("]", atIndex: Int(arc4random_uniform(i)))
}
return String(bracks)
}output:
randBrack(2) // "]][["Random check balance function:
func randIsBal(n: Int) {
let (bal, un) = ("", "un")
for str in (1...n).map(randBrack) {
print("\(str) is \(isBal(str) ? bal : un)balanced\n")
}
}
randIsBal(4)output:
// ][ is unbalanced
//
// ]][[ is unbalanced
//
// []][[] is unbalanced
//
// [][][[]] is balancedTcl
proc generate {n} {
if {!$n} return
set l [lrepeat $n "\[" "\]"]
set len [llength $l]
while {$len} {
set tmp [lindex $l [set i [expr {int($len * rand())}]]]
lset l $i [lindex $l [incr len -1]]
lset l $len $tmp
}
return [join $l ""]
}
proc balanced s {
set n 0
foreach c [split $s ""] {
# Everything unmatched is ignored, which is what we want
switch -exact -- $c {
"\[" {incr n}
"\]" {if {[incr n -1] < 0} {return false}}
}
}
expr {!$n}
}
for {set i 0} {$i < 15} {incr i} {
set s [generate $i]
puts "\"$s\"\t-> [expr {[balanced $s] ? {OK} : {NOT OK}}]"
}Sample output:
"" -> OK "][" -> NOT OK "]][[" -> NOT OK "]]][[[" -> NOT OK "[][][[]]" -> OK "[[[][[]]]]" -> OK "[][][[][]][]" -> OK "[[]][]]]][[[][" -> NOT OK "][][[][][][[]]][" -> NOT OK "][[[][]][]]][][[][" -> NOT OK "]][][]][[][[][[]][][" -> NOT OK "[[[][[][]]][]]][[]]][[" -> NOT OK "[[]]][]][[[[]]][[][][[]]" -> NOT OK "][[][][]][[[]][[[[][]]]][]" -> NOT OK "]][[][[][[[[]][[][]][[]]]]][" -> NOT OK
Constructing correctly balanced strings
It is, of course, possible to directly construct such a balanced string, this being much more useful as the length of the string to generate grows longer. This is done by conceptually building a random tree (or forest) and then walking the tree, with open brackets being appended when a node is entered from its root and close brackets being appended when a node is left for its root. This is equivalent to inserting a balanced pair of brackets at a random place in an initially-empty string times, which might be done like this:
proc constructBalancedString {n} {
set s ""
for {set i 0} {$i < $n} {incr i} {
set x [expr {int(rand() * ([string length $s] + 1))}]
set s "[string range $s 0 [expr {$x-1}]]\[\][string range $s $x end]"
}
return $s
}As noted, because the generated string is guaranteed to be balanced, it requires no further filtering and this results in much more efficient generation of balanced strings at longer lengths (because there's no need to backtrack).
TMG
Unix TMG is designed to process and generate files rather than process text in memory. Therefore generation and analysis parts can only be done in separate programs.
Generation program in Unix TMG:
program: readint(n) [n>0] readint(seed)
loop: parse(render) [--n>0?]/done loop;
render: random(i, 15) [i = (i+1)*2] loop2 = { 1 * };
loop2: random(b, 2) ( [b&1?] ={<[>} | ={<]>} ) [--i>0?]/done loop2 = { 2 1 };
done: ;
/* Reads decimal integer */
readint: proc(n;i) string(spaces) [n=0] inta
int1: [n = n*12+i] inta\int1;
inta: char(i) [i<72?] [(i =- 60)>=0?];
/* LCG params: a = 29989, c = 28411, m = 35521 */
random: proc(r,mod) [seed = (seed*72445 + 67373) % 105301]
[r = seed % mod] [r = r<0 ? -r : r];
spaces: <<
>>;
n: 0; i: 0; b: 0; seed: 0;Sample output:
[][] ][]][]][[[]]]]][]][] [[][]][[[]]]][[[ []][[[[]][[]][]]][][]] ]]]][[[[
Analysis can be done easily using grammar specification, rather than counting brackets:
loop: parse(corr)\loop parse(incorr)\loop;
corr: brkts * = { < OK: > 1 * };
brkts: brkt/null brkts = { 2 1 };
brkt: <[> brkts <]> = { <[> 1 <]> };
null: = {};
incorr: smark ignore(<<>>) any(!<<>>) string(nonl) scopy ( * | () )
= { <NOT OK: > 1 * };
nonl: !<<
>>;Sample output:
NOT OK: ][][
NOT OK: ]][][[
OK: [[]][][]
NOT OK: [[][]]][][]][]
OK: [[[]][[]][][]][]
OK: [[]][[[][]]][[[]]]
NOT OK: [[[[][[][[][[[]]][[[[[][]]
OK: [[[][[[][][[[[[]]][[][]][]][][[[]]]]]]]]
TUSCRIPT
$$ MODE TUSCRIPT
SECTION gen_brackets
values="[']",brackets=""
LOOP n=1,12
brackets=APPEND (brackets,"","~")
LOOP m=1,n
a=RANDOM_NUMBERS (1,2,1),br=SELECT(values,#a)
brackets=APPEND(brackets,"",br)
b=RANDOM_NUMBERS (1,2,1),br=SELECT(values,#b)
brackets=APPEND(brackets,"",br)
ENDLOOP
ENDLOOP
brackets=SPLIT (brackets,":~:")
ENDSECTION
MODE DATA
$$ BUILD X_TABLE brackets=*
[[[[ (4 ]]]] )4
[[[ (3 ]]] )3
[[ (2 ]] )2
[ (1 ] )1
$$ MODE TUSCRIPT
DO gen_brackets
LOOP b=brackets
status=CHECK_BRACKETS (b,brackets,a1,e1,a2,e2)
PRINT b," ",status
ENDLOOPOutput:
OK ]] ERROR [[]] OK [][[]] OK []]]][[] ERROR []][]][][[ ERROR [[]][][]]]]] ERROR []][[][[]][[][ ERROR [][[[][[[[[[]][[ ERROR ]]][[]][]][[[][][[ ERROR ][][[]]][[[[[]]][[][ ERROR [[[][][]][]]]][[[[[[]] ERROR ][[[]][[][[[[[[[[[[[]]]] ERROR
TXR
@(define paren)@(maybe)[@(coll)@(paren)@(until)]@(end)]@(end)@(end)
@(do (defvar r (make-random-state nil))
(defun generate-1 (count)
(let ((bkt (repeat "[]" count)))
(cat-str (shuffle bkt))))
(defun generate-list (num count)
[[generate tf (op generate-1 count)] 0..num]))
@(next :list @(generate-list 22 6))
@(output)
INPUT MATCHED REST
@(end)
@ (collect)
@ (all)
@parens
@ (and)
@{matched (paren)}@mismatched
@ (end)
@ (output)
@{parens 15} @{matched 15} @{mismatched 15}
@ (end)
@(end)The recursive pattern function @(paren) gives rise to a grammar which matches parentheses:
@(define paren)@(maybe)[@(coll)@(paren)@(until)]@(end)]@(end)@(end)
A string of balanced parentheses is an optional unit (@(maybe) ... @(end)) that begins with [, followed by zero or more such balanced strings, followed by ].
Sample run:
$ ./txr paren.txr INPUT MATCHED REST ][[[]][][[]] ][[[]][][[]] []][[]][][[] [] ][[]][][[] [][[[[]]]]][ [] [[[[]]]]][ ][[][[]]][][ ][[][[]]][][ [[[][[]]][]] [[[][[]]][]] ]][]][[[][[] ]][]][[[][[] [[]][]][[[]] [[]] []][[[]] ]][]][]][[[[ ]][]][]][[[[ ]][[]]][][[[ ]][[]]][][[[ ]]]][[]][[[[ ]]]][[]][[[[ ][[[[][[]]]] ][[[[][[]]]] ][]][]]][[[[ ][]][]]][[[[ ]][][[][][[] ]][][[][][[] ]][][]][[][[ ]][][]][[][[ [][[]][]]][[ [] [[]][]]][[ [[]]]]][[[[] [[]] ]]][[[[] ]][[[[[[]]]] ]][[[[[[]]]] ][][][[[]][] ][][][[[]][] []][]][][][[ [] ][]][][][[ ]][[[][]][[] ]][[[][]][[] ][[[[]]]][][ ][[[[]]]][][ [[]]]]][[][[ [[]] ]]][[][[
TypeScript
// Balanced brackets
function isStringBalanced(str: string): bool {
var paired = 0;
for (var i = 0; i < str.length && paired >= 0; i++) {
var c = str.charAt(i);
if (c == '[')
paired++;
else if (c == ']')
paired--;
}
return (paired == 0);
}
function generate(n: number): string {
var opensCount = 0, closesCount = 0;
// Choose at random until n of one type generated
var generated: string[] = new Array(); // Works like StringBuilder
while (opensCount < n && closesCount < n) {
if (Math.floor(Math.random() * 2) == 0) {
++opensCount;
generated.push("[");
} else {
++closesCount;
generated.push("]");
}
}
// Now pad with the remaining other brackets
generated.push(opensCount == n ?
"]".repeat(n - closesCount) :
"[".repeat(n - opensCount));
return generated.join("");
}
console.log("Supplied examples");
var tests: string[] = ["", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"];
for (var test of tests)
console.log(`The string '${test}' is ${(isStringBalanced(test) ? "OK." : "not OK."));
console.log();
console.log("Random generated examples");
for (var example = 0; example < 10; example++) {
var test = generate(Math.floor(Math.random() * 10) + 1);
console.log(`The string '${test}' is ${(isStringBalanced(test) ? "OK." : "not OK.")}`);
}- Output:
Supplied examples The string '' is OK. The string '[]' is OK. The string '][' is not OK. The string '[][]' is OK. The string '][][' is not OK. The string '[[][]]' is OK. The string '[]][[]' is not OK. Random generated examples The string ']]][[[][' is not OK. The string '][][][[[[]]]' is not OK. The string ']][[[[]]' is not OK. The string '][]]]]]][][][][[[[[[' is not OK. The string '][[[][][[[]]]]' is not OK. The string '[[[]]]' is OK. The string ']]]][[[[[]' is not OK. The string '][[]]]]][[[][[]]][[[' is not OK. The string ']]]][]][[[[[' is not OK. The string '[[[[[[]]]]]]' is OK.
UNIX Shell
generate() {
local b=()
local i j tmp
for ((i=1; i<=$1; i++)); do
b+=( '[' ']')
done
for ((i=${#b[@]}-1; i>0; i--)); do
j=$(rand $i)
tmp=${b[j]}
b[j]=${b[i]}
b[i]=$tmp
done
local IFS=
echo "${b[*]}"
}
# a random number in the range [0,n)
rand() {
echo $(( $RANDOM % $1 ))
}
balanced() {
local -i lvl=0
local i
for ((i=0; i<${#1}; i++)); do
case ${1:i:1} in
'[') ((lvl++));;
']') (( --lvl < 0 )) && return 1;;
esac
done
(( lvl == 0 )); return $?
}
for ((i=0; i<=10; i++)); do
test=$(generate $i)
balanced "$test" && result=OK || result="NOT OK"
printf "%s\t%s\n" "$test" "$result"
done- Output:
OK ][ NOT OK []][ NOT OK [[][]] OK ]][[]][[ NOT OK [[]][[][]] OK []][[[[]]]][ NOT OK [[]][]][]][[[] NOT OK [][][[[[][][]]]] OK [][][[[[]]][[][]]] OK ][[]][][][[[]]][[]][ NOT OK
Ursala
#import std
#import nat
balanced = @NiX ~&irB->ilZB ~&rh?/~&lbtPB ~&NlCrtPX
#cast %bm
main = ^(2-$'[]'*,balanced)* eql@ZFiFX*~ iota64output:
< '': true, '[]': true, '][[]': false, '[][]': true, '[[]]': true, ']][[[]': false, '][][[]': false, '[]][[]': false, '][[][]': false, '[][][]': true, '[[]][]': true, '][[[]]': false, '[][[]]': true, '[[][]]': true, '[[[]]]': true>
VBA
Public Function checkBrackets(s As String) As Boolean
'function checks strings for balanced brackets
Dim Depth As Integer
Dim ch As String * 1
Depth = 0
For i = 1 To Len(s)
ch = Mid$(s, i, 1)
If ch = "[" Then Depth = Depth + 1
If ch = "]" Then
If Depth = 0 Then 'not balanced
checkBrackets = False
Exit Function
Else
Depth = Depth - 1
End If
End If
Next
checkBrackets = (Depth = 0)
End Function
Public Function GenerateBrackets(N As Integer) As String
'generate a string with N opening and N closing brackets in random order
Dim s As String
Dim N2 As Integer, j As Integer
Dim Brackets() As String * 1
Dim temp As String * 1
'catch trivial value
If N <= 0 Then
GenerateBrackets = ""
Exit Function
End If
N2 = N + N
ReDim Brackets(1 To N2)
For i = 1 To N2 Step 2
Brackets(i) = "["
Brackets(i + 1) = "]"
Next i
'shuffle.
For i = 1 To N2
j = 1 + Int(Rnd() * N2)
'swap brackets i and j
temp = Brackets(i)
Brackets(i) = Brackets(j)
Brackets(j) = temp
Next i
'generate string
s = ""
For i = 1 To N2
s = s & Brackets(i)
Next i
GenerateBrackets = s
End Function
Public Sub BracketsTest()
Dim s As String
Dim i As Integer
For i = 0 To 10
s = GenerateBrackets(i)
Debug.Print """" & s & """: ";
If checkBrackets(s) Then Debug.Print " OK" Else Debug.Print " Not OK"
Next
End Subsample output:
BracketsTest "": OK "][": Not OK "[][]": OK "][[]][": Not OK "][]][[[]": Not OK "[[][]]][[]": Not OK "]][[[[[]]]][": Not OK "[[[]][][][][]]": OK "]][[[]][[[]][]][": Not OK "[[][]][]]][[[[]][]": Not OK "]][][[[][]]][][[][][": Not OK
VBScript
For n = 1 To 10
sequence = Generate_Sequence(n)
WScript.Echo sequence & " is " & Check_Balance(sequence) & "."
Next
Function Generate_Sequence(n)
For i = 1 To n
j = Round(Rnd())
If j = 0 Then
Generate_Sequence = Generate_Sequence & "["
Else
Generate_Sequence = Generate_Sequence & "]"
End If
Next
End Function
Function Check_Balance(s)
Set Stack = CreateObject("System.Collections.Stack")
For i = 1 To Len(s)
char = Mid(s,i,1)
If i = 1 Or char = "[" Then
Stack.Push(char)
ElseIf Stack.Count <> 0 Then
If char = "]" And Stack.Peek = "[" Then
Stack.Pop
End If
Else
Stack.Push(char)
End If
Next
If Stack.Count > 0 Then
Check_Balance = "Not Balanced"
Else
Check_Balance = "Balanced"
End If
End Function- Output:
Note: For some reason, the function to generate the bracket sequence, Generate_Sequence, does not produce a balanced one. But the function to check if it is balanced or not, Check_Balance, works if a balanced argument is passed manually.
] is Not Balanced. ]] is Not Balanced. [[] is Not Balanced. []]] is Not Balanced. [[]][ is Not Balanced. ]][][] is Not Balanced. ][][[]] is Not Balanced. [[]]]]][ is Not Balanced. ]][][]][] is Not Balanced. [[][[[[[]] is Not Balanced.
Antother version not using libraries. The generator works as intended (more difficult to do than the checking)
option explicit
function do_brackets(bal)
dim s,i,cnt,r
if bal then s="[":cnt=1 else s="":cnt=0
for i=1 to 20
if (rnd>0.7) then r=not r
if not r then
s=s+"[" :cnt=cnt+1
else
if not bal or (bal and cnt>0) then s=s+"]":cnt=cnt-1
end if
next
if bal and cnt<>0 then s=s&string(cnt,"]")
if not bal and cnt=0 then s=s&"]"
do_brackets=s
end function
function isbalanced(s)
dim s1,i,cnt: cnt=0
for i=1 to len(s)
s1=mid(s,i,1)
if s1="[" then cnt=cnt+1
if s1="]" then cnt=cnt-1
if cnt<0 then isbalanced=false:exit function
next
isbalanced=(cnt=0)
end function
function iif(a,b,c): if a then iif=b else iif=c end if : end function
randomize timer
dim i,s,bal,bb
for i=1 to 10
bal=(rnd>.5)
s=do_brackets(bal)
bb=isbalanced(s)
wscript.echo iif (bal,"","un")& "balanced string " &vbtab _
& s & vbtab & " Checks as " & iif(bb,"","un")&"balanced"
nextSample run
unbalanced string [[[[[[[[][[][[[[[]][ Checks as unbalanced balanced string [[[]]][[[[[[[]][]]]]]] Checks as balanced balanced string [[[]][]][[[[[]]]]] Checks as balanced unbalanced string ][][]][[[[]]][]]]]]] Checks as unbalanced balanced string [[][[[[[[[[]]][[[[[[[]]]]]]]]]]]]] Checks as balanced balanced string [[]][][[[[[]]]]] Checks as balanced balanced string [][[]][][][[[[[[]]]]]] Checks as balanced balanced string [[[[[[[]][[[[[[[[[][[]]]]]]]]]]]]]]] Checks as balanced unbalanced string [[]]][[[[[[]]]]]][][] Checks as unbalanced balanced string [[[[[[][[[[[]]]]]]]]]] Checks as balanced
Visual Basic .NET
Module Module1
Private rand As New Random
Sub Main()
For numInputs As Integer = 1 To 10 '10 is the number of bracket sequences to test.
Dim input As String = GenerateBrackets(rand.Next(0, 5)) '5 represents the number of pairs of brackets (n)
Console.WriteLine(String.Format("{0} : {1}", input.PadLeft(10, CChar(" ")), If(IsBalanced(input) = True, "OK", "NOT OK")))
Next
Console.ReadLine()
End Sub
Private Function GenerateBrackets(n As Integer) As String
Dim randomString As String = ""
Dim numOpen, numClosed As Integer
Do Until numOpen = n And numClosed = n
If rand.Next(0, 501) Mod 2 = 0 AndAlso numOpen < n Then
randomString = String.Format("{0}{1}", randomString, "[")
numOpen += 1
ElseIf rand.Next(0, 501) Mod 2 <> 0 AndAlso numClosed < n Then
randomString = String.Format("{0}{1}", randomString, "]")
numClosed += 1
End If
Loop
Return randomString
End Function
Private Function IsBalanced(brackets As String) As Boolean
Dim numOpen As Integer = 0
Dim numClosed As Integer = 0
For Each character As Char In brackets
If character = "["c Then numOpen += 1
If character = "]"c Then
numClosed += 1
If numClosed > numOpen Then Return False
End If
Next
Return numOpen = numClosed
End Function
End Module- Output:
][[][]][ : NOT OK
[]]][[[] : NOT OK
[[]][] : OK
[] : OK
[[[]]] : OK
[] : OK
[]][][ : NOT OK
]][[[] : NOT OK
: OK
[] : OK
V (Vlang)
import datatypes as dt
fn is_valid(bracket string) bool {
mut s := dt.Stack<string>{}
for b in bracket.split('') {
if b == '[' {
s.push(b)
} else {
if s.peek() or {''} == '[' {
s.pop() or {panic("WON'T GET HERE EVER")}
} else {
return false
}
}
}
return true
}
fn main() {
brackets := ['','[]','[][]','[[][]]','][','][][','[]][[]','[][[][[]][][[][]]]']
for b in brackets {
println('$b ${is_valid(b)}')
}
}- Output:
true [] true [][] true [[][]] true ][ false ][][ false []][[] false [][[][[]][][[][]]] true
Wren
import "random" for Random
var isBalanced = Fn.new { |s|
if (s.isEmpty) return true
var countLeft = 0 // number of left brackets so far unmatched
for (c in s) {
if (c == "[") {
countLeft = countLeft + 1
} else if (countLeft > 0) {
countLeft = countLeft - 1
} else {
return false
}
}
return countLeft == 0
}
System.print("Checking examples in task description:")
var brackets = ["", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"]
for (b in brackets) {
System.write((b != "") ? b : "(empty)")
System.print("\t %(isBalanced.call(b) ? "OK" : "NOT OK")")
}
System.print("\nChecking 7 random strings of brackets of length 8:")
var rand = Random.new()
for (i in 1..7) {
var s = ""
for (j in 1..8) s = s + ((rand.int(2) == 0) ? "[" : "]")
System.print("%(s) %(isBalanced.call(s) ? "OK" : "NOT OK")")
}- Output:
Checking examples in task description: (empty) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK Checking 7 random strings of brackets of length 8: [][][][[ NOT OK [[][][]] OK [[[[]]]] OK [[]]]][[ NOT OK ]][][[]] NOT OK ][]][[[] NOT OK [][][[][ NOT OK
X86 Assembly
section .data
MsgBalanced: db "OK", 10
MsgBalancedLen: equ 3
MsgUnbalanced: db "NOT OK", 10
MsgUnbalancedLen: equ 7
MsgBadInput: db "BAD INPUT", 10
MsgBadInputLen: equ 10
Open: equ '['
Closed: equ ']'
section .text
BalancedBrackets:
xor rcx, rcx
mov rsi, rdi
cld
processBracket:
lodsb
cmp al, 0
je determineBalance
cmp al, Open
je processOpenBracket
cmp al, Closed
je processClosedBracket
mov rsi, MsgBadInput
mov rdx, MsgBadInputLen
jmp displayResult
processOpenBracket:
add rcx, 1
jmp processBracket
processClosedBracket:
cmp rcx, 0
je unbalanced
sub rcx, 1
jmp processBracket
determineBalance:
cmp rcx, 0
jne unbalanced
mov rsi, MsgBalanced
mov rdx, MsgBalancedLen
jmp displayResult
unbalanced:
mov rsi, MsgUnbalanced
mov rdx, MsgUnbalancedLen
displayResult:
mov rax, 1
mov rdi, 1
syscall
retXBasic
' Balanced brackets
PROGRAM "balancedbrackets"
VERSION "0.001"
IMPORT "xst"
DECLARE FUNCTION Entry()
INTERNAL FUNCTION IsStringBalanced(str$)
INTERNAL FUNCTION Generate$(n%%)
' Pseudo-random number generator
' Based on the rand, srand functions from Kernighan & Ritchie's book
' 'The C Programming Language'
DECLARE FUNCTION Rand()
DECLARE FUNCTION SRand(seed%%)
FUNCTION Entry()
PRINT "Supplied examples"
DIM tests$[6]
tests$[0] = ""
tests$[1] = "[]"
tests$[2] = "]["
tests$[3] = "[][]"
tests$[4] = "][]["
tests$[5] = "[[][]]"
tests$[6] = "[]][[]"
FOR example@@ = 0 TO UBOUND(tests$[])
test$ = tests$[example@@]
PRINT "The string '"; test$; "' is ";
IFT IsStringBalanced(test$) THEN
PRINT "OK."
ELSE
PRINT "not OK."
END IF
NEXT example@@
PRINT
PRINT "Random generated examples"
XstGetSystemTime (@msec)
SRand(INT(msec) MOD 32768)
FOR example@@ = 1 TO 10
test$ = Generate$(INT(Rand() / 32768.0 * 10.0) + 1)
PRINT "The string '"; test$; "' is ";
IFT IsStringBalanced(test$) THEN
PRINT "OK."
ELSE
PRINT "not OK."
END IF
NEXT example@@
END FUNCTION
FUNCTION IsStringBalanced(s$)
paired& = 0
i%% = 1
DO WHILE i%% <= LEN(s$) && paired& >= 0
c$ = MID$(s$, i%%, 1)
SELECT CASE c$
CASE "[":
INC paired&
CASE "]":
DEC paired&
END SELECT
INC i%%
LOOP
END FUNCTION (paired& = 0)
FUNCTION Generate$(n%%)
opensCount%% = 0
closesCount%% = 0
' Choose at random until n%% of one type generated
generated$ = ""
DO WHILE opensCount%% < n%% && closesCount%% < n%%
SELECT CASE (INT(Rand() / 32768.0 * 2.0) + 1)
CASE 1:
INC opensCount%%
generated$ = generated$ + "["
CASE 2:
INC closesCount%%
generated$ = generated$ + "]"
END SELECT
LOOP
' Now pad with the remaining other brackets
IF opensCount%% = n%% THEN
generated$ = generated$ + CHR$(']', n%% - closesCount%%)
ELSE
generated$ = generated$ + CHR$('[', n%% - opensCount%%)
END IF
END FUNCTION generated$
' Return pseudo-random integer on 0..32767
FUNCTION Rand()
#next&& = #next&& * 1103515245 + 12345
END FUNCTION USHORT(#next&& / 65536) MOD 32768
' Set seed for Rand()
FUNCTION SRand(seed%%)
#next&& = seed%%
END FUNCTION
END PROGRAM- Output:
Supplied examples The string '' is OK. The string '[]' is OK. The string '][' is not OK. The string '[][]' is OK. The string '][][' is not OK. The string '[[][]]' is OK. The string '[]][[]' is not OK. Random generated examples The string '[[]][][[[]]]' is OK. The string '[]' is OK. The string '[]]][[' is not OK. The string ']]][][[]][][[[' is not OK. The string ']]]]]][[[][[][[[' is not OK. The string '[]][' is not OK. The string ']]][[][][[' is not OK. The string '][' is not OK. The string '[[]][][]' is OK. The string '[[[][[]]]]' is OK.
XBS
const Chars:[string] = ["[","]"];
func GenerateString(Amount:number=4):string{
set Result:string = "";
<|(*1..Amount)=>Result+=Chars[math.random(0,?Chars-1)];
send Result;
}
func IsBalanced(String:string):boolean{
set Pairs:number = 0;
<|(*(0..(?String-1)))=>(String::at(_)=="[")?(Pairs<0)?=>send false,Pairs++,=>Pairs--;
send (Opens==Closes)&(Pairs==0);
}
repeat 10 {
set s = GenerateString(math.random(2,4)*2);
log(`{s}: {IsBalanced(s)}`);
}- Output:
][]][]: false ][]]]]: false ][][: false [[[[]][]: false [[][]]: true [[]]: true ]][][][[: false [][]: true ][[[[]: false []]][]: false
XPL0
include c:\cxpl\codes; \intrinsic code declarations
int N, I, C, Nest;
char Str;
[\Generate a string with N open brackets and N close brackets in arbitrary order
N:= IntIn(0); \get number of brackets/2 from keyboard
Str:= Reserve(2*N);
for I:= 0 to 2*N-1 do Str(I):= ^[;
C:= 0; \initialize count of "]"
repeat I:= Ran(2*N); \change N random locations to "]"
if Str(I) # ^] then [Str(I):= ^]; C:= C+1];
until C>=N;
\Determine whether string consists of nested pairs of open/close brackets
I:= 0; C:= 0; Nest:= false;
while I<2*N do
[if Str(I) = ^[ then C:= C+1 else C:= C-1;
if C<0 then Nest:= true;
ChOut(0,Str(I));
I:= I+1;
];
ChOut(0,9\tab\);
if Nest then Text(0,"NOT ");
Text(0,"OK
");
]Example output:
2 []][ NOT OK [][] OK 3 [[][]] OK
Ya
@Balanced[]s // each source must be started by specifying its file name; std extension .Ya could be ommitted and auto added by compiler
// all types are prefixed by `
// definition of anything new is prefixed by \, like \MakeNew_[]s and \len
// MakeNew_[]s is Ok ident in Ya: _ starts sign part of ident, which must be ended by _ or alphanum
`Char[^] \MakeNew_[]s(`Int+ \len) // `Char[^] and `Char[=] are arrays that owns their items, like it's usally in other langs;
// yet in assignment of `Char[^] to `Char[=] the allocated memory is moved from old to new owner, and old string becomes empty
// there are tabs at starts of many lines; these tabs specify what in C++ is {} blocks, just like in Python
len & 1 ==0 ! // it's a call to postfix function '!' which is an assert: len must be even
`Char[=] \r(len) // allocate new string of length len
// most statements are analogous to C++ but written starting by capital letter: For If Switch Ret
For `Char[] \eye = r; eye // // `Char[] is a simplest array of chars, which does not hold a memory used by array items; inc part of For loop is missed: it's Ok, and condition and init could also be missed
*eye++ = '['; *eye++ = '[' // fill r by "[][][]...". The only place with ; as statement delemiter: required because the statement is not started at new line.
// below is a shuffle of "[][][]..." array
For `Char[] \eye = r; ++eye // var eye is already defined, but being the same `Char[] it's Ok by using already exisiting var. ++eye is used: it allows use of eye[-1] inside
`Int+ \at = Random(eye/Length) // `Int+ is C++'s unsigned int. eye/Length: / is used for access to field, like in file path
eye[-1],eye[at] = eye[at],eye[-1] // swap using tuples; eye[-1] accesses char that is out of current array, yet it's allowed
Ret r // Ret is C's return
`Bool \AreBalanced(`Char[] \brackets)
`Int+ \extra = 0
For ;brackets ;++brackets
Switch *brackets
'[' // it's a C++'s 'case': both 'case' and ':' are skipped being of no value; but the code for a case should be in block, which is here specifyed by tabs at next line start
++extra
']'
If !!extra // '!!' is `Bool not, like all other `Bool ops: && || ^^
Ret No // No and False are C's false; Yes and True are C's true
--extra
// There is no default case, which is written as ':' - so if no case is Ok then it will fail just like if being written as on the next line
// : { 0! } // C's default: assert(0);
Ret extra == 0
// function ala 'main' is not used: all global code from all modules are executed; so below is what typically is in ala 'main'
For `Int \n=10; n; --n
// below note that new var 'brackets' is created inside args of func call
//@Std/StdIO/ is used here to use Print function; else it maybe changed to Use @Std/StdIO at global level before this For loop
@Std/StdIO/Print(; "%s : %s\n" ;`Char[=] \brackets = MakeNew_[]s(10) /* all bracket strings are of length 10 */; AreBalanced(brackets) ? "Ok" : "bad")
// note that starting arg of Print is missed by using ';' - default arg value is allowed to use for any arg, even if next args are writtenYabasic
sub check_brackets(s$)
local level, i
for i = 1 to len(s$)
switch mid$(s$, i, 1)
case "[": level = level + 1 : break
case "]": level = level - 1 : if level < 0 break 2
end switch
next i
return level = 0
end sub
s$ = "[[]][]"
print s$, " = ";
if not check_brackets(s$) print "not ";
print "ok"Zig
const std = @import("std");
const print = std.debug.print;
const max_pairs = 256;
pub fn is_balanced(buf: []u8) bool {
var count: usize = 0;
for (buf) |ch| switch (ch) {
'[' => count += 1,
']' => {
if (count == 0) return false;
count -= 1;
},
else => return false,
};
return count == 0;
}
pub fn main() !void {
for (0..10) |n_pairs| {
if (n_pairs > max_pairs)
return error.MaximumNumberOfPairsExceded;
var buf: [2 * max_pairs]u8 = undefined;
for (0..n_pairs) |i| buf[i] = '[';
for (n_pairs..n_pairs * 2) |i| buf[i] = ']';
const rand = std.crypto.random;
const len = n_pairs * 2;
const reps = 2;
for (0..len * reps) |i_rep| {
const i = i_rep % len;
const j = rand.int(usize) % len;
const temp = buf[i];
buf[i] = buf[j];
buf[j] = temp;
}
const s = buf[0..len];
print("'{s}': {}\n", .{ s, is_balanced(s) });
}
}- Output:
'': true '][': false '][[]': false '[[]]][': false '[]][[][]': false ']]][[[]][[': false '][[[[[]]]][]': false '[[[[]]][][][]]': true '][]]][[[][[[]][]': false '[]][[[][[][]]][][]': false
zkl
fcn bb(bs){ while(a:=bs.span("[","]")) {bs=bs[a[1],*]} (Void!=a) }The span method finds the start and length of a balanced span. This algorithm assumes the string only contains brackets; a matched span is chopped off the front of the string and a new balanced span is searched for. Stops when the string is empty or unbalanced (span returns Void).
zkl: bb("")
True
zkl: bb("[]")
True
zkl: bb("[][]")
True
zkl: bb("[[][]]")
True
zkl: bb("][")
False
zkl: bb("][][")
False
zkl: bb("[]][[]")
False
ZX Spectrum Basic
10 FOR n=1 TO 7
20 READ s$
25 PRINT "The sequence ";s$;" is ";
30 GO SUB 1000
40 NEXT n
50 STOP
1000 LET s=0
1010 FOR k=1 TO LEN s$
1020 LET c$=s$(k)
1030 IF c$="[" THEN LET s=s+1
1040 IF c$="]" THEN LET s=s-1
1050 IF s<0 THEN PRINT "Bad!": RETURN
1060 NEXT k
1070 IF s=0 THEN PRINT "Good!": RETURN
1090 PRINT "Bad!"
1100 RETURN
2000 DATA "[]","][","][][","[][]","[][][]","[]][[]","[[[[[]]]]][][][]][]["