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
<lang 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’))</lang>
- 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
<lang 360asm>* 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</lang>
- Output:
1 ][[[][[] ? 2 ]][]][][[[[][[ ? 3 [] ok 4 ][ ? 5 ][[][]]]]] ? 6 ][]] ? 7 ]][][][]]] ? 8 [[[[][[[[][[]] ? 9 ][[]][[[[[[[[[]]][ ? 10 ]]]][][[][]]][][[[ ? 11 [][[]][][][[[] ? 12 ]] ? 13 [][[[]]] ok 14 ][ ? 15 []][ ? 16 ][[]][]]][[] ? 17 ][][]] ? 18 [] ok 19 [[[[[[][[[[[][][ ? 20 [[][[][] ?
ABAP
<lang 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( ).
</lang>
- Output:
[[]][[]]]] => NOT OK ][]][[][][ => NOT OK [][]]][[[] => NOT OK ][][[[][[] => NOT OK [[[][]]][] => OK ][][]][[[[ => NOT OK ][][[[[]][ => NOT OK ][[][]][[] => NOT OK [[]][[]][] => OK [][]]][]]] => NOT OK
Action!
<lang 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</lang>
- 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
<lang Acurity Architect> 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 </lang>
- 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: <lang Ada>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;</lang>
Output:
Brackets : TRUE []: TRUE ][: FALSE []][: FALSE ][][: FALSE ][][: FALSE [[]]][: FALSE [][][]: TRUE []]][[: FALSE ][][][: FALSE ]]][[[[]: FALSE [[[]][]]: TRUE [][][]][: FALSE [[][]]][: FALSE []]]][[[: FALSE
Aime
<lang 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;
}</lang> Sample output:
is balanced ][ is unbalanced ]][[ is unbalanced ]]][[[ is unbalanced [[]][][] is balanced [[][]][][] is balanced []]]][][[][[ is unbalanced ][[[]][[][]]][ is unbalanced [][[[][[]]]]][][ is unbalanced [[][[[[][]]][][]]] is balanced
ALGOL 68
<lang algol68># 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</lang>
- 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
ANTLR
Java
<lang> 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' ; </lang> 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.
<lang APL>gen ← (⊂+?+)⍨ ⌷ ('[]'/⍨⊢) bal ← (((|≡⊢)+\) ∧ 0=+/)(+⌿1 ¯1×[1]'[]'∘.=⊢)</lang>
Sample run for 0..N..10:
<lang APL> ↑{br←gen ⍵ ⋄ br,': ',(1+bal br)⊃'Bad' 'Good'}¨0,⍳10
- Good
[]: Good ][][: Bad [][[]]: Good []]][[][: Bad ][][[[[]]]: Bad ][][][][][[]: Bad ][[[][[][]][]]: Bad [[][[]]][[[[]]]]: Good [[[]][[[[][]][]]]]: Good ]][][][][[][][]][[[]: Bad</lang>
AppleScript
(ES6 functionally composed version)
<lang AppleScript>-- 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</lang> Sample output:
'][' problem
^
'[][[' problem
^
'[[][]]' OK
'][][[][[' problem
^
'[]][][[][]' problem
^
'[[[][]]]][][' problem
^
ARM Assembly
<lang 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, lr
</lang>
Arturo
<lang rebol>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" ]</lang>
- Output:
[] OK [[[] Not OK [][][] OK [[][[]]] OK [[[[[][[]] Not OK [[]][[[]]][] OK ][[]][][[[[[[] Not OK ]][[]]][[[]]][]] Not OK ][[[[[[]]][]]][][] Not OK []][][][]]][[[[][][] Not OK
AutoHotkey
<lang 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" }</lang> Output:
][ - NOT OK ][ - NOT OK [][] - OK [[]] - OK []][[] - NOT OK ]][[[] - NOT OK ][[]][][ - NOT OK [][[[]]] - OK [][]]][[[] - NOT OK [[][[]]][] - OK
A second example repeatedly replacing []: <lang AutoHotkey>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" }</lang> Sample output:
[] - True ][ - False ]][[ - False []][ - False [[]]][ - False ]][[[] - False [][]]][[ - False []][][][ - False [[[][]][]] - True [][][[[]]] - True
AutoIt
<lang 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 $cnt < 0 Then Return SetError(1,0,0) Next Return 1 EndFunc </lang>
AWK
<lang AWK>#!/usr/bin/awk -f BEGIN {
print isbb("[]")
print isbb("][")
print isbb("][][")
print isbb("[][]")
print isbb("[][][]")
print isbb("[]][[]")
}
function isbb(x) {
s = 0
for (k=1; k<=length(x); k++) {
c = substr(x,k,1) if (c=="[") {s++} else { if (c=="]") s-- }
if (s<0) {return 0}
}
return (s==0)
} </lang> Output:
1 0 0 1 1 0
BaCon
<lang bacon>FOR len = 0 TO 18 STEP 2
str$ = ""
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</lang>
- Output:
OK: OK: [] BAD: ]][] OK: [[]][] OK: [[[][]]] BAD: ][[][]]][] BAD: ]][[]][[[][[ OK: [[][][][][][]] BAD: [[[]]]][[[[[][]] BAD: ][][][][[[[[][]]][
BASIC
<lang qbasic>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</lang>
Sample output:
[][[][][]] OK
][[[]] NOT OK
[][] OK
[]][][][[] NOT OK
[][[]][[]] OK
][][[] NOT OK
][[] NOT OK
][][[]][][ NOT OK
][[[][]] NOT OK
][][[[]] NOT OK
][[]][ NOT OK
OK
Commodore BASIC
Based on ZX Spectrum BASIC implementation <lang basic>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 , [], ][, [][], ][][, [[][]], []][[]</lang>
BASIC256
<lang 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 function</lang>
Batch File
Uses the rewrite rule "[]" -> null to check if brackets are balanced.
<lang dos>:: 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</lang>
- 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
<lang bbcbasic>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."</lang>
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. <lang Befunge>v > "KO TON" ,,,,,, v > ~ : 25*- #v_ $ | > 25*, @
> "KO" ,, ^
> : 1991+*+- #v_ v
> \ : 1991+*+- #v_v
\ $
^ < <$<</lang>
BQN
Balanced brackets are a monoid with the following presentation:
⟨l, r | l·r = e⟩
This allows for a particular simple implementation:
<lang bqn>Gen ← (•rand.Deal⊏⥊⟜"[]") 2⊸× Bal ← {
Mul ← {a‿b𝕊x‿y: ⟨a+0⌈x-b, y+0⌈b-x⟩}
0‿0 ≡ 0‿0("]["⊸=⊸Mul)´𝕩
}</lang>
- Output:
(⊢≍Bal¨) Gen¨5⥊3
┌─
╵ "]][][[" "[][][]" "][][[]" "[[][]]" "][[][]"
0 1 0 1 0
┘
Bracmat
Bracmat has no 'random' function, so the shuffle is a bit improvised. A variable someNumber is initialised with a big number is repeatedly divided by the number of '['s in the test string until zero. The remainders are used as index to partition and swap the first half of the test string. Then the second half and first half are also swapped. The test whether the test string is balanced is simple, but not very efficient.
<lang bracmat>( (bal=|"[" !bal "]" !bal)
& ( generate
= a j m n z N S someNumber
. !arg:<1&
| 11^123+13^666+17^321:?someNumber
& (!arg:?n)+1:?N
& :?S
& whl
' (!n+-1:~<0:?n&"[" "]" !S:?S)
& whl
' ( !someNumber:>0
& mod$(!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
)
);</lang> Output:
:Balanced ][:Not balanced [][]:Balanced [][[]]:Balanced [[[]]]][:Not balanced ]]]][][[[[:Not balanced [[][[[]]][]]:Balanced [][]][]]]][[[[:Not balanced [][]][[[]]][][][:Not balanced [][[[[]][]]][[[]]]:Balanced [][[][]][]]][][[[]][:Not balanced
Brat
<lang 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" }
}</lang>
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
<lang 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;
}</lang>result:<lang>: True '[]': True ']][[': False '[][][]': True '[]][[]][': False '[]][[[[]]]': False ']]]][[[]][[[': False ']]]]]][][[[[[[': False '[][]][[][[[]]][]': False</lang>
C#
<lang csharp>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 ");
}
}
}</lang> Sample output:
"" is balanced. "[]" is balanced. "[]][" is not balanced. "[][][]" is balanced. "[[[]][]]" is balanced. "[][[][[]]]" is balanced. "[]][][][[][]" is not balanced. "[]]][][]][[][[" is not balanced. "[]]][]]][[][[][[" is not balanced.
<lang csharp>
// 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");
</lang>
C++
<lang cpp>#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";
}
}</lang> Output:
ok: ok: [] ok: [][] bad: []][[] ok: [[[]][]] bad: ][[[[]][]] ok: [[[]][[]][]] bad: ]][[]][[[[][]] bad: [[]]]][]][[][[[]
Ceylon
<lang 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);</lang>
Output:
- OK [] - OK ][[] - NOT OK ][[]][ - NOT OK []]][[][ - NOT OK [[[][][]]] - OK [[][]][[]][] - OK [[][[[]]][]][] - OK ]][[][][[][]][[] - NOT OK [[]]]]]]][[[[][][[ - NOT OK [[]][[]][[]]]][[[]][ - NOT OK
Clojure
<lang 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)))))</lang>
There are other ways to express the balanced? function.
- We can use
reduceto consume the sequence:
- <lang Clojure>(defn balanced? [s]
(empty?
(reduce
(fn [stack first]
(case first
\[ (conj stack \[)
\] (if (seq stack)
(pop stack)
(reduced [:UNDERFLOW]))))
'()
s)))</lang>
- Only
[s are put on the stack. We can just count the unmatched ones.
- <lang Clojure>(defn balanced? [s]
(let [opens-closes (->> s
(map {\[ 1, \] -1})
(reductions + 0))]
(and (not-any? neg? opens-closes) (zero? (last opens-closes))))) </lang>
Output:
user> (->> (range 10)
(map gen-brackets ,)
(map (juxt identity balanced?) ,)
vec)
[["" true]
["[]" true]
["[[]]" true]
["[][[]]" true]
["[]][][][" nil]
["[[[[[]]]]]" true]
["]][[][][[[]]" nil]
["[]]]][[[[]][][" nil]
["][][[]]][[][][][" nil]
["][][]]][]][[[][[[]" nil]
CLU
<lang 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</lang>
- Output:
"": balanced "[]": balanced "[][]": balanced "[[]][]": balanced "[[]][[]]": balanced "][[]][][[]": not balanced "[][][]][]][[": not balanced "][]][]]][][[[[": not balanced "[][[]][][][[[]]]": balanced "][[][][]][[]][][[]": not balanced "]]]][[[[]][][][[][[]": not balanced
COBOL
<lang 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.</lang>
CoffeeScript
<lang 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
</lang> output <lang> > coffee balanced.coffee [[[[ false [[[] false [[][ false [[]] true [][[ false [][] true []][ false []]] false ][[[ false ][[] false ][][ false ][]] false ]][[ false ]][] false ]]][ false ]]]] false </lang>
Common Lisp
<lang 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))))
</lang>
Output:
CL-USER> (show-balanced-brackets) T : NIL: ][ T : [[]] NIL: []]][[ T : [][][][] NIL: []][]][[[] NIL: []]]]][][[[[ NIL: ][]]]]][[[[][[ T : [[[[[[][[]]]]]]] NIL: ]][[[[][]][[[[]]]]
Component Pascal
BlackBox Component Builder <lang oberon2> 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.
</lang>
Execute: ^Q Brackets.Do [] [][] [[][]] ][ ][][ []][[]~
Output:
[] :> $TRUE [][] :> $TRUE [[][]] :> $TRUE ][ :> $FALSE ][][ :> $FALSE []][[]:> $FALSE
Crystal
<lang ruby>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</lang>
Output:
: true []: true ][][: false ][[]][: false []]][][[: false ][[]][[[]]: false []]][[[]][[]: false [[][[[][]]]]][: false [[[]]]][][][][[]: false [[][][]][][[]][][]: true
D
Standard Version
D standard library has a function for this. <lang d>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);
}
}</lang>
- Output:
OK: [] bad: []][ OK: [][][] bad: [][]]][[ OK: [[[]][]][] bad: ][][[[][][]] bad: [[]][[]]]]][[[ bad: ][]]][[[[][][][]
Imperative Version
<lang d>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);
}
}</lang> The output is similar.
Functional Style
<lang d>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);
}
}</lang>
Delphi
<lang 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;</lang>
[]: OK [[]]: OK [][][]: OK [[[]][]]: OK ]]]][[[[[]: not OK ][[][][[[]]]: not OK [][[]]][[][[]]: not OK [[[[[]][]][[]]]]: OK []]][][[[[[]][]][]: not OK
Déjà Vu
<lang dejavu>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? "[]][[]"</lang>
- Output:
true true true true false false false
EchoLisp
<lang scheme> (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)
❌ "[]]][[][" ❌ "]][][[[]" ❌ "][[[]]][" 👍 "[][[[]]]" ❌ "]][[][][" ❌ "][][[[]]" 👍 "[][][[]]" ❌ "]][[][[]" ❌ "[[]]][[]" ❌ "[[][]]]["
</lang>
Elena
ELENA 4.x : <lang elena>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==$91).iif(1,-1)) < 0);
^ (0 == counter)
}
}
public program() {
for(int len := 0, len < 9, len += 1)
{
var str := randomBrackets(len);
console.printLine("""",str,"""",str.isBalanced ? " is balanced" : " is not balanced")
};
console.readChar()
}</lang>
- Output:
"" is balanced "[]" is balanced "][[]" is not balanced "[[[]]]" is balanced "][[[]]][" is not balanced "[]]]][[[][" is not balanced "[[]][][[]]][" is not balanced "[][]]]]][[[[][" is not balanced "][]]][[[[][[][]]" is not balanced "][]][][[]]][[[]][[" is not balanced
Elixir
<lang elixir>defmodule Balanced_brackets do
def task do
Enum.each(0..5, fn n ->
brackets = generate(n)
result = is_balanced(brackets) |> task_balanced
IO.puts "#{brackets} is #{result}"
end)
end
defp generate( 0 ), do: []
defp generate( n ) do
for _ <- 1..2*n, do: Enum.random ["[", "]"]
end
def is_balanced( brackets ), do: is_balanced_loop( brackets, 0 )
defp is_balanced_loop( _, n ) when n < 0, do: false
defp is_balanced_loop( [], 0 ), do: true
defp is_balanced_loop( [], _n ), do: false
defp is_balanced_loop( ["[" | t], n ), do: is_balanced_loop( t, n + 1 )
defp is_balanced_loop( ["]" | t], n ), do: is_balanced_loop( t, n - 1 )
defp task_balanced( true ), do: "OK"
defp task_balanced( false ), do: "NOT OK"
end
Balanced_brackets.task</lang>
- Output:
is OK [[ is NOT OK [][] is OK ]][]][ is NOT OK [[][][]] is OK [][[][[]]] is OK
Erlang
<lang Erlang> -module( balanced_brackets ). -export( [generate/1, is_balanced/1, task/0] ).
generate( N ) -> [generate_bracket(random:uniform()) || _X <- lists:seq(1, 2*N)].
is_balanced( String ) -> is_balanced_loop( String, 0 ).
task() -> lists:foreach( fun (N) -> String = generate( N ), Result = is_balanced( String ), io:fwrite( "~s is ~s~n", [String, task_balanced(Result)] ) end, lists:seq(0, 5) ).
is_balanced_loop( _String, N ) when N < 0 -> false; is_balanced_loop( [], 0 ) -> true; is_balanced_loop( [], _N ) -> false; is_balanced_loop( [$[ | 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". </lang>
- Output:
47> balanced_brackets:task(). is OK [[ is NOT OK [][] is OK [[[[][ is NOT OK []]]]][[ is NOT OK [[[][[[[]] is NOT OK
Euphoria
<lang 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 for</lang>
Sample 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)
<lang lisp>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
)
)
)
)</lang>
and also assuming the following generic bindings in the Name Manager for the WorkBook:
<lang lisp>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()
)
)
)</lang>
- 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#
<lang fsharp>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)</lang>
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
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. <lang Factor>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</lang>
Some more idiomatic solution might be as follows:
<lang Factor>USING: io formatting locals kernel math sequences unicode.case ; IN: balanced-brackets
- map-braces ( -- qout )
[
{
{ "[" [ drop 1 ] }
{ "]" [ drop -1 ] }
[ drop 0 ]
} case
]
- balanced? ( str -- ? )
map-braces map sum 0 =
"[1+2*[3+4*[5+6]-3]*4-[3*[3+3]]]" balanced? -- Data stack: t </lang>
Fantom
<lang 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")
}
}
}
} </lang>
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
<lang 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[]</lang>
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: <lang fortran> ! $ 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 </lang>
FreeBASIC
<lang 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</lang> 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
Gambas
Click this link to run this code <lang gambas>'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</lang> 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
<lang 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</lang>
Go
<lang 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("()")
}</lang> 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: <lang groovy>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)
}</lang>
Check Balance of Bracket String: <lang groovy>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)
}
}</lang>
Test: <lang groovy>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}"
}</lang>
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. <lang haskell> isMatching :: String -> Bool isMatching = null . foldl aut []
where
aut ('[':s) ']' = s
-- aut ('{':s) '}' = s -- automaton could be extended
aut s x = x:s
</lang>
This generates an infinite stream of correct balanced brackets expressions:
<lang haskell>brackets = filter isMatching
$ [1.. ] >>= (`replicateM` "[]{}") </lang>
λ> take 10 brackets
["[]","{}","[[]]","[][]","[]{}","[{}]","{[]}","{{}}","{}[]","{}{}"]
In case the index of unmatched opening bracket is need to be found, following solution is suitable.
<lang haskell> 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</lang>
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. <lang haskell>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</lang>
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:
<lang haskell>import Control.Applicative ((<|>)) import Data.List (findIndex, replicate, scanl) import Data.List.Split (chunksOf) import System.Random
BALANCED BRACKETS -------------------
bracketProblemIndex :: String -> Maybe Int bracketProblemIndex s =
findIndex (< 0) depths <|> unClosed
where
depths = nesting s
unClosed
| 0 /= last depths = Just $ pred (length s)
| otherwise = Nothing
nesting :: String -> [Int] nesting = tail . scanl level 0
where level n '[' = succ n level n ']' = pred n level n _ = n
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 _ = ']'</lang>
- Output:
]][]][: Unmatched
^
][[][[: Unmatched
^
][][[[: Unmatched
^
]][][]: Unmatched
^
[[][]]: OK
]]][]]: Unmatched
^
[][][[: Unmatched
^
[]]]]]: Unmatched
^
][[][[: Unmatched
^
[][]][: Unmatched
^
Icon and Unicon
<lang Icon>procedure main(arglist) every s := genbs(!arglist) do
write(image(s), if isbalanced(s) then " is balanced." else " is unbalanced")
end
procedure isbalanced(s) # test if a string is balanced re: [] return (s || " ") ? (bal(,'[',']') = *s+1) end
procedure genbs(i) # generate strings of i pairs of [] s := "" every 1 to i do s ||:= "[]" # generate i pairs every !s := ?s # shuffle return s end</lang>
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: <lang j>bracketDepth =: '[]' -&(+/\)/@:(=/) ] checkBalanced =: _1 -.@e. bracketDepth genBracketPairs =: (?~@# { ])@#"0 1&'[]' NB. bracket pairs in arbitrary order</lang> Examples:<lang j> (, ' ' , ('bad';'OK') {::~ checkBalanced)"1 genBracketPairs i. 10
OK
][ bad
][[] bad
[[[]]] OK
[][[]][] OK
[][[[][]]] OK
[]][]][]][[[ bad
[[]][[][][]][] OK
]]]][[][][[[[]][ bad
[]]][][][[[[]][[]] bad</lang>
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
<lang java5>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));
}
}
}</lang> 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
<lang java>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)); } } }</lang>
- 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
<lang JavaScript>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')
}</lang>
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
<lang JavaScript> 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;
} </lang>
- 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: <lang JavaScript>(() => {
'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();
})();</lang>
- Output:
'' OK
'[]' OK
'[][[' problem
^
'[]]][[' problem
^
'[][[][[[' problem
^
'[][[[]][]]' OK
']]][[][][][]' problem
^
Julia
<lang 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</lang>
- Output:
pass
][ fail
[][] pass
][[]][ fail
[[[]]][] pass
]]]][[[][[ fail
]]][[][][[[] fail
]][]][][[[][][ fail
[]][]]]][[[][[[] fail
One-line version: <lang julia>balancedbrackets(str::AbstractString) = foldl((x, y) -> x < 0 ? -1 : x + y, collect((x == '[') - (x == ']') for x in str), init = 0) == 0</lang>
K
<lang 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))
</lang>
Klingphix
<lang>"[[]][]]"
%acc 0 !acc %flag false !flag
len [
get tochar dup "[" == [$acc 1 + !acc] if "]" == [$acc 1 - !acc] if $acc 0 < [true !flag] if ] for
$acc 0 # $flag or ( [" is NOT ok"] [" is OK"] ) if print
" " input</lang>
Kotlin
<lang scala>import java.util.Random
fun isBalanced(s: String): Boolean {
if (s.isEmpty()) return true
var countLeft = 0 // number of left brackets so far unmatched
for (c in s) {
if (c == '[') countLeft++
else if (countLeft > 0) countLeft--
else return false
}
return countLeft == 0
}
fun main(args: Array<String>) {
println("Checking examples in task description:")
val brackets = arrayOf("", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]")
for (b in brackets) {
print(if (b != "") b else "(empty)")
println("\t " + if (isBalanced(b)) "OK" else "NOT OK")
}
println()
println("Checking 7 random strings of brackets of length 8:")
val r = Random()
(1..7).forEach {
var s = ""
for (j in 1..8) {
s += if (r.nextInt(2) == 0) '[' else ']'
}
println("$s " + if (isBalanced(s)) "OK" else "NOT OK")
}
}</lang> 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++
<lang lisp>(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))))</lang>
Lasso
<lang 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)</lang>
- Output:
[] = true ][[] = false ]][[[] = false ][][[][] = false [[[]][[]]] = true ]]]][[[[][[] = false [[[[[[]]]]]][] = true [[]][][]][]][[[] = false [[[]][[[]][]]][[]] = true
Liberty BASIC
<lang lb> 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
end </lang>
Supplied 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
<lang 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)) </lang>
Maple
This functionality is provided by Maple. <lang 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 := "[[]][[[[[[[[[]][][]]"
false
</lang> Furthermore, Maple can check whether multiple fences are balanced in the same string. <lang Maple> > StringTools:-IsBalanced( "[()()]", "[(", "])" );
true
</lang>
Mathematica/Wolfram Language
<lang mathematica>(* 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."]])</lang>
MATLAB / Octave
<lang matlab>function x = isbb(s)
t = cumsum((s=='[') - (s==']')); x = all(t>=0) && (t(end)==0);
end; </lang> 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
<lang 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</lang>
Mercury
<lang 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)
).
</lang>
MiniScript
We start by defining a function:
<lang MiniScript>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</lang>
We can evaluate the example strings with this code:
<lang MiniScript>examples = [ "", "[]", "[][]", "[[][]]", "][", "][][", "[]][[]", "[[[]"]
for str in examples balanced = isBalanced(str) if balanced then outcome = "is OK" else outcome = "NOT OK" print """" + str + """ " + outcome end for</lang>
- 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. <lang modula2> 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. </lang>
- Output:
[]][[]][ no [[[]]] yes ][ no ][]][[ no [][[]] yes ][[] no [][] yes ][][]][[ no [] yes []][[][] no
Nanoquery
<lang 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</lang>
- 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
<lang 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")</lang>
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
Oberon-2
<lang oberon2> 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. </lang>
- Output:
[]:> TRUE [][]:> TRUE [[][]]:> TRUE ][:> FALSE ][][:> FALSE []][[]:> FALSE
Objeck
<lang 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();
}
}
} </lang>
: true []: true [][]: true [[][]]: true ][: false ][][: false []][[]: false
OCaml
<lang 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);
- </lang>
$ ocaml balanced_brackets.ml 3 []][[] false $ ocaml balanced_brackets.ml 3 [[]][] true
Oforth
<lang 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) ;</lang>
- Output:
#[ genBrackets(5) dup print " -->" print isBalanced println ] times(10) [[][[]][]] -->-1 ][][][][][ -->0 ][[][][]][ -->0 ][[]][[]][ -->0 [][][][][] -->-1 ]]][][][[[ -->0 [[[[[]]]]] -->-1 [[[[[]]]]] -->-1 ][][][][][ -->0 ]]][][][[[ -->0
ooRexx
<lang 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
</lang> 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
<lang 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 "][" '0 </lang>
PARI/GP
<lang parigp>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")))</lang>
Pascal
See Delphi
Perl
Idiomatic solution, using a regex that performs subpattern recursion (works with Perl 5.10 and newer):
<lang Perl>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";
}</lang>
- Output:
ok: '' ok: '[]' bad: '[]][' bad: ']][][[' ok: '[[]][[]]' bad: '[[[][]]]][' bad: '][[[]][]][[]' ok: '[[]][[[][[]]]]' bad: ']][]]][[][][[][['
If input strings are allowed to contain unrelated characters, this can be extended to:
<lang Perl>sub balanced {
shift =~ /^ ( [^\[\]]++ | \[ (?1)* \] )* $/x;
}</lang>
Regexp::Common::balanced can give such a regexp too (non-bracket chars allowed). Its recent versions use the subpattern recursion and are hence also only for Perl 5.10 and up.
<lang Perl>use Regexp::Common 'balanced'; my $re = qr/^$RE{balanced}{-parens=>'[]'}$/; sub balanced {
return shift =~ $re;
}</lang>
Alternative implementation, using straightforward depth counting:
<lang Perl>sub balanced {
my $depth = 0;
for (split //, shift) {
if ($_ eq '[') { ++$depth }
elsif ($_ eq ']') { return if --$depth < 0 }
}
return !$depth
}</lang>
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
<lang 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 print</lang>
PHP
The sample is given as unix shell script, you need to have php-cli (or what your package manager calls it) installed.
<lang PHP>#!/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);
} </lang> Sample run:
OK [][] OK [[]] OK []][ NOT OK ][][[] NOT OK [][[]] OK ][[[]] NOT OK ]][[][][ NOT OK []][][[] NOT OK ][]]][[[ NOT OK [[[][]]] OK
Picat
Foreach loop
<lang picat>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(["","[]", "[][]", "[[][]]", "][",
"][][", "[]][[]", "[][][][][][][][][][]",
"[[[[[[[]]]]]]]", "[[[[[[[]]]]]]",
"[][[]][]","[[][]][]", "[][][[]][]"]).</lang>
- 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). <lang Picat>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.</lang>
PicoLisp
<lang 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")) )</lang>
Output:
[] OK [[]] OK ]]][[[not OK [[[][]]] OK [][][[[]]] OK []][[[][[]]]not OK [[[]]][][][][] OK ]][][[[[]][]]][[not OK []][][[[][[]]][]][not OK [[[][]]]]][][[]]][[[not OK
PL/I
<lang pli>*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;</lang>
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
<lang 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
}
</lang> <lang PowerShell>
- Test
$Strings = @( "" ) $Strings += 1..5 | ForEach { ( [char[]]("[]" * $_) | Get-Random -Count ( $_ * 2 ) ) -join "" }
ForEach ( $String in $Strings )
{
$String.PadRight( 12, " " ) + (Get-BalanceStatus $String)
}
</lang>
- Output:
OK [] OK ]][[ NOT OK ]][][[ NOT OK [[[][]]] OK ][[[]][][] NOT OK
PowerShell (Regex Version)
<lang PowerShell> function Test-BalancedBracket {
<#
.SYNOPSIS
Tests a string for balanced brackets.
.DESCRIPTION
Tests a string for balanced brackets. ("<>", "[]", "{}" or "()")
.EXAMPLE
Test-BalancedBracket -Bracket Brace -String '{abc(def[0]).xyz}'
Test a string for balanced braces.
.EXAMPLE
Test-BalancedBracket -Bracket Curly -String '{abc(def[0]).xyz}'
Test a string for balanced curly braces.
.EXAMPLE
Test-BalancedBracket -Bracket Curly -String ([System.IO.File]::ReadAllText('.\Foo.ps1'))
Test a file for balanced curly braces.
.LINK
http://go.microsoft.com/fwlink/?LinkId=133231
#>
[CmdletBinding()]
[OutputType([bool])]
Param
(
[Parameter(Mandatory=$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 $s) {'Is balanced.'} else {'Is not balanced.'})"
} </lang>
- Output:
(Empty) : Is balanced. [] : Is balanced. ][ : Is not balanced. [][] : Is balanced. ][][ : Is not balanced. [[][]] : Is balanced. []][[] : Is not balanced.
Prolog
DCG are very usefull for this kind of exercice ! <lang Prolog>rosetta_brackets :- test_brackets([]), test_brackets(['[',']']), test_brackets(['[',']','[',']']), test_brackets(['[','[',']','[',']',']']), test_brackets([']','[']), test_brackets([']','[',']','[']), test_brackets(['[',']',']','[','[',']']).
balanced_brackets :- gen_bracket(2, B1, []), test_brackets(B1), gen_bracket(4, B2, []), test_brackets(B2), gen_bracket(4, B3, []), test_brackets(B3), gen_bracket(6, B4, []), test_brackets(B4), gen_bracket(6, B5, []), test_brackets(B5), gen_bracket(8, B6, []), test_brackets(B6), gen_bracket(8, B7, []), test_brackets(B7), gen_bracket(10, B8, []), test_brackets(B8), gen_bracket(10, B9, []), test_brackets(B9).
test_brackets(Goal) :- ( Goal = [] -> write('(empty)'); maplist(write, Goal)), ( balanced_brackets(Goal, []) -> writeln(' succeed') ; writeln(' failed') ).
% grammar of balanced brackets balanced_brackets --> [].
balanced_brackets --> ['['], balanced_brackets, [']'].
balanced_brackets --> ['[',']'], balanced_brackets.
% generator of random brackets
gen_bracket(0) --> [].
gen_bracket(N) --> {N1 is N - 1, R is random(2)}, bracket(R), gen_bracket(N1).
bracket(0) --> ['[']. bracket(1) --> [']']. </lang> Sample output :
?- balanced_brackets. [[ failed [[][ failed [[]] succeed [[][]] succeed [][[][ failed ][]][[[] failed [[[[]][] failed [[[[[][[]] failed []][[[][]] failed true .
Test with Rosetta examples :
?- rosetta_brackets. (empty) succeed [] succeed [][] succeed [[][]] succeed ][ failed ][][ failed []][[] failed true.
PureBasic
<lang PureBasic>Procedure.s Generate(N)
For i=1 To N
sample$+"[]"
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
Next</lang> Output sample
[] is balanced. [[]] is balanced. [[[]]] is balanced. [][]]][[ is not balanced [][][][]][ is not balanced
Python
Procedural
<lang python>>>> 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 balanced</br></br>==='"`UNIQ--h-112--QINU`"' Functional ===</br>Works with: [[SMW" contains a listed "[" character as part of the property label and has therefore been classified as invalid.Python version 3.2
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.
<lang python>>>> 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 balanced</lang>
Array 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.
<lang python>>>> 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 balanced</lang>
Qi
<lang qi>(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 "[]][[]")
</lang>
Quackery
<lang 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 ]</lang>
- 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
<lang r>balanced <- function(str){
str <- strsplit(str, "")1 str <- ifelse(str=='[', 1, -1) all(cumsum(str) >= 0) && sum(str) == 0
}</lang>
Alternately, using perl 5.10-compatible regexps,
<lang r>balanced <- function(str) {
regexpr('^(\\[(?1)*\\])*$', str, perl=TRUE) > -1
}</lang>
To generate some some examples:
<lang R>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)
}))</lang>
Output: <lang r> balanced parens 1 FALSE ][][ 2 FALSE [][[]]][[]][]]][[[ 3 FALSE ][[][][]][][[] 4 FALSE ][][][][][][][ 5 TRUE [[[][]]][[[][][]]] 6 TRUE [] 7 FALSE ]][[][[] 8 FALSE []]]][[[]][[[] 9 TRUE [[[[][[][]]]]] 10 TRUE []</lang>
Racket
<lang 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)) </lang>
Raku
(formerly Perl 6) There's More Than One Way To Do It.
Depth counter
<lang perl6>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($s) ?? "is" !! "is not"} well-balanced"</lang>
FP oriented
Here's a more idiomatic solution using a hyperoperator to compare all the characters to a backslash (which is between the brackets in ASCII), a triangle reduction to return the running sum, a given to make that list the topic, and then a topicalized junction and a topicalized subscript to test the criteria for balance. <lang perl6>sub balanced($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"</lang>
String munging
Of course, a Perl 5 programmer might just remove as many inner balanced pairs as possible and then see what's left.
<lang perl6>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";</lang>
Parsing with a grammar
<lang perl6>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";</lang>
Red
<lang 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"]] ]</lang>
REXX
with 40 examples
<lang rexx>/*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.*/</lang>
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
<lang rexx> /*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 */
</lang>
- 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.
<lang rexx>/*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 r</lang>
output when using the default input:
125476 expressions were checked, 23713 were balanced, 101763 were unbalanced.
Ring
<lang 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." </lang> 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.
Ruby
<lang 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
end</lang>
One output:
OK: OK: [] bad: []][ OK: [[][]] bad: []]][][[ bad: ][]][[[[]] bad: []]][[]][[[] bad: ][[][]][][[]][ OK: [][[][[[]][]][]] bad: []][][]][[[[[][]]] bad: [[] bad: []] OK: a[ letters[-1] ].xyz[0]
Run BASIC
<lang runbasic>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 i</lang>
One output:
OK
OK [[[][]]]
OK [[[]][[[][[][]]]]]
Not OK ][][]][[
OK [][][]
Not OK [][]][]][[]]][[[
Not OK ]][[[[]]]][]]][[[[
OK [[][[[]]][]]
Not OK []][][][[[]]
Not OK ][]][[
Not OK []][][][[]
Rust
<lang 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())
}
}</lang>
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
<lang scala>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))
}</lang>
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
<lang scala>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
}
}</lang>
Alternate implementation of "isBalanced" using tail-recursion instead of var and return:
<lang scala>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)
}
</lang>
Slightly modified implementation of "isBalanced" using tail-recursion
<lang scala> @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))
}
} </lang>
Sample output:
- ok [ - NOT ok [] - ok [][ - NOT ok ][][ - NOT ok [][][ - NOT ok [][][] - ok [[[]][] - NOT ok [[][][]] - ok [[[][]][] - NOT ok
Scheme
<lang 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 "[]][[]") </lang>
Scilab
<lang>function varargout=isbb(s)
st=strsplit(s); t=cumsum((st=='[')-(st==']')); balanced=and(t>=0) & t(length(t))==0; varargout=list(balanced)
endfunction</lang>
- 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().
<lang>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);
end</lang> Console output:
][]][ F [[[[][[[][]]]]]] T ][[][]]]][]][[]][][]]] F
Seed7
<lang 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;</lang>
Output:
: TRUE : TRUE : TRUE []: TRUE ][: FALSE ][: FALSE ][[]: FALSE [[]]: TRUE [[]]: TRUE [][][]: TRUE [[][]]: TRUE []]][[: FALSE [][][]][: FALSE [][][][]: TRUE ]][][[][: FALSE
Sidef
<lang ruby>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)
}</lang>
- Output:
NOT balanced : ] NOT balanced : [ NOT balanced : [[] NOT balanced : ][] balanced : [[]] NOT balanced : [[]]]][][]] balanced : x[ y [ [] z ]][ 1 ][]abcd
Simula
<lang 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</lang>
- 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
<lang sml>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 rest</lang>
An example of usage
<lang sml>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 *)
["", "[]", "[][]", "[[][]]", "][", "][][", "[]][[]"]
)</lang>
Output:
OK [] OK [][] OK [[][]] OK ][ NOT OK ][][ NOT OK []][[] NOT OK
Stata
<lang 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) } end</lang>
Test
: is_balanced("")
1
: is_balanced("[]")
1
: is_balanced("[][]")
1
: is_balanced("[[][]]")
1
: is_balanced("][")
0
: is_balanced("][][")
0
: is_balanced("[]][[]")
Swift
Checks balance function:
<lang swift>import Foundation
func isBal(str: String) -> Bool {
var count = 0
return !str.characters.contains { ($0 == "[" ? ++count : --count) < 0 } && count == 0
} </lang>output:<lang swift> isBal("[[[]]]") // true
isBal("[]][[]") // false
</lang>Random Bracket function:<lang swift>
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)
}
</lang>output:<lang swift>
randBrack(2) // "]][["
</lang>Random check balance function:<lang swift>
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)
</lang>output:<lang swift>
// ][ is unbalanced // // ]][[ is unbalanced // // []][[] is unbalanced // // [][][[]] is balanced</lang>
Tcl
<lang tcl>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 $s] ? {OK} : {NOT OK}}]"
}</lang> Sample output:
"" -> OK "][" -> NOT OK "]][[" -> NOT OK "]]][[[" -> NOT OK "[][][[]]" -> OK "[[[][[]]]]" -> OK "[][][[][]][]" -> OK "[[]][]]]][[[][" -> NOT OK "][][[][][][[]]][" -> NOT OK "][[[][]][]]][][[][" -> NOT OK "]][][]][[][[][[]][][" -> NOT OK "[[[][[][]]][]]][[]]][[" -> NOT OK "[[]]][]][[[[]]][[][][[]]" -> NOT OK "][[][][]][[[]][[[[][]]]][]" -> NOT OK "]][[][[][[[[]][[][]][[]]]]][" -> NOT OK
Constructing correctly balanced strings
It is, of course, possible to directly construct such a balanced string, this being much more useful as the length of the string to generate grows longer. This is done by conceptually building a random tree (or forest) and then walking the tree, with open brackets being appended when a node is entered from its root and close brackets being appended when a node is left for its root. This is equivalent to inserting a balanced pair of brackets at a random place in an initially-empty string times, which might be done like this: <lang tcl>proc constructBalancedString {n} {
set s ""
for {set i 0} {$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
}</lang> 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: <lang UnixTMG>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;</lang>
Sample output:
[][] ][]][]][[[]]]]][]][] [[][]][[[]]]][[[ []][[[[]][[]][]]][][]] ]]]][[[[
Analysis can be done easily using grammar specification, rather than counting brackets: <lang UnixTMG>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: !<< >>;</lang>
Sample output:
NOT OK: ][][
NOT OK: ]][][[
OK: [[]][][]
NOT OK: [[][]]][][]][]
OK: [[[]][[]][][]][]
OK: [[]][[[][]]][[[]]]
NOT OK: [[[[][[][[][[[]]][[[[[][]]
OK: [[[][[[][][[[[[]]][[][]][]][][[[]]]]]]]]
TUSCRIPT
<lang 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 ENDLOOP </lang> Output:
OK ]] ERROR [[]] OK [][[]] OK []]]][[] ERROR []][]][][[ ERROR [[]][][]]]]] ERROR []][[][[]][[][ ERROR [][[[][[[[[[]][[ ERROR ]]][[]][]][[[][][[ ERROR ][][[]]][[[[[]]][[][ ERROR [[[][][]][]]]][[[[[[]] ERROR ][[[]][[][[[[[[[[[[[]]]] ERROR
TXR
<lang 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)</lang>
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 ][[[]][][[]] ][[[]][][[]] []][[]][][[] [] ][[]][][[] [][[[[]]]]][ [] [[[[]]]]][ ][[][[]]][][ ][[][[]]][][ [[[][[]]][]] [[[][[]]][]] ]][]][[[][[] ]][]][[[][[] [[]][]][[[]] [[]] []][[[]] ]][]][]][[[[ ]][]][]][[[[ ]][[]]][][[[ ]][[]]][][[[ ]]]][[]][[[[ ]]]][[]][[[[ ][[[[][[]]]] ][[[[][[]]]] ][]][]]][[[[ ][]][]]][[[[ ]][][[][][[] ]][][[][][[] ]][][]][[][[ ]][][]][[][[ [][[]][]]][[ [] [[]][]]][[ [[]]]]][[[[] [[]] ]]][[[[] ]][[[[[[]]]] ]][[[[[[]]]] ][][][[[]][] ][][][[[]][] []][]][][][[ [] ][]][][][[ ]][[[][]][[] ]][[[][]][[] ][[[[]]]][][ ][[[[]]]][][ [[]]]]][[][[ [[]] ]]][[][[
UNIX Shell
<lang bash>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</lang>
- Output:
OK ][ NOT OK []][ NOT OK [[][]] OK ]][[]][[ NOT OK [[]][[][]] OK []][[[[]]]][ NOT OK [[]][]][]][[[] NOT OK [][][[[[][][]]]] OK [][][[[[]]][[][]]] OK ][[]][][][[[]]][[]][ NOT OK
Ursala
<lang Ursala>#import std
- import nat
balanced = @NiX ~&irB->ilZB ~&rh?/~&lbtPB ~&NlCrtPX
- cast %bm
main = ^(2-$'[]'*,balanced)* eql@ZFiFX*~ iota64</lang> output:
< '': true, '[]': true, '][[]': false, '[][]': true, '[[]]': true, ']][[[]': false, '][][[]': false, '[]][[]': false, '][[][]': false, '[][][]': true, '[[]][]': true, '][[[]]': false, '[][[]]': true, '[[][]]': true, '[[[]]]': true>
VBA
<lang vb> Public Function checkBrackets(s As String) As Boolean 'function checks strings for balanced brackets Dim Depth As Integer Dim ch As String * 1
Depth = 0 For i = 1 To Len(s)
ch = Mid$(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 Sub </lang>
sample output:
BracketsTest "": OK "][": Not OK "[][]": OK "][[]][": Not OK "][]][[[]": Not OK "[[][]]][[]": Not OK "]][[[[[]]]][": Not OK "[[[]][][][][]]": OK "]][[[]][[[]][]][": Not OK "[[][]][]]][[[[]][]": Not OK "]][][[[][]]][][[][][": Not OK
VBScript
<lang vb>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</lang>
- 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) <lang vb> 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"
next </lang> Sample 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
<lang vbnet>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</lang>
- Output:
][[][]][ : NOT OK
[]]][[[] : NOT OK
[[]][] : OK
[] : OK
[[[]]] : OK
[] : OK
[]][][ : NOT OK
]][[[] : NOT OK
: OK
[] : OK
Wren
<lang ecmascript>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")")
}</lang>
- 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
<lang X86Assembly> 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 ret
</lang>
XBasic
<lang xbasic> 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 </lang>
- 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
<lang 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)}`); }</lang>
- Output:
][]][]: false ][]]]]: false ][][: false [[[[]][]: false [[][]]: true [[]]: true ]][][][[: false [][]: true ][[[[]: false []]][]: false
XPL0
<lang 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 "); ]</lang>
Example output:
2 []][ NOT OK [][] OK 3 [[][]] OK
Ya
<lang 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 written</lang>
Yabasic
<lang Yabasic>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"</lang>
zkl
<lang zkl>fcn bb(bs){ while(a:=bs.span("[","]")) {bs=bs[a[1],*]} (Void!=a) }</lang> 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
<lang zxbasic>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 "[]","][","][][","[][]","[][][]","[]][[]","[[[[[]]]]][][][]][][" </lang>