Balanced brackets: Difference between revisions
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===String munging=== |
===String munging=== |
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Of course, a Perl 5 programmer might just remove as many inner balanced pairs as possible and then see what's left. |
Of course, a Perl 5 programmer might just remove as many inner balanced pairs as possible and then see what's left. |
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{{works with|Rakudo|2015.12}} |
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<lang perl6>sub balanced($_ is copy) { |
<lang perl6>sub balanced($_ is copy) { |
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Nil while s:g/'[]'//; |
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$_ eq ''; |
$_ eq ''; |
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} |
} |
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Revision as of 23:23, 6 January 2016
You are encouraged to solve this task according to the task description, using any language you may know.
Task:
- Generate a string with opening brackets (“
[”) and 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.
Examples:
(empty) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK
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
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>integer unbalanced(text s) {
integer b, i;
b = 0;
i = 0;
while (i < length(s)) {
if (s[i] == '[') {
b += 1;
} else {
b -= 1;
if (b < 0) {
break;
}
}
i += 1; }
return b;
}
text generate(integer d) {
integer i; text s;
i = d;
while (i) {
s = insert(s, 0, '[');
i -= 1;
}
i = d;
while (i) {
s = insert(s, drand(length(s)), ']');
i -= 1;
}
return s;
}
integer main(void) {
integer i;
i = 0;
while (i < 10) {
text s;
s = generate(i);
o_text(s);
o_text(" is ");
if (unbalanced(s)) {
o_text("un");
}
o_text("balanced\n");
i += 1; }
return 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 ']'
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 $cnt < 0 Then Return SetError(1,0,0) Next Return 1 EndFunc </lang>
AWK
<lang AWK>#!/usr/bin/awk -f BEGIN {
print isbb("[]")
print isbb("][")
print isbb("][][")
print isbb("[][]")
print isbb("[][][]")
print isbb("[]][[]")
}
function isbb(x) {
s = 0
for (k=1; k<=length(x); k++) {
c = substr(x,k,1) if (c=="[") {s++} else { if (c=="]") s-- }
if (s<0) {return 0}
}
return (s==0)
} </lang> Output:
1 0 0 1 1 0
BASIC
<lang qbasic>DECLARE FUNCTION checkBrackets% (brackets AS STRING) DECLARE FUNCTION generator$ (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
Batch File
Uses a Markov algorithm/code "[]" -> null to check if brackets are balanced.
<lang dos>:: Balanced Brackets Task from Rosetta Code Wiki
- Batch File Implementation
@echo off setlocal enabledelayedexpansion
- The Main Thing...
set numofpairs=10 set howmanystrings=10 cls for /l %%. in (1,1,%howmanystrings%) do ( call :generate call :checkforbalance ) echo.&pause&exit /b
- /The Main Thing.
- Generate strings of brackets...
- generate
set i=0&set j=%numofpairs%&set samp= set /a toss=%random%%%2 set put1=[&set put2=] if %toss%==1 (set put1=]&set put2=[) for /l %%x in (1,1,%numofpairs%) do ( set samp=!samp!%put1% ) :add if not %i%==%numofpairs% ( set /a rnd=%random%%%%j%+1 set /a oppos=%j%-!rnd! ::A new trick for substitution of delayed variables... for /f "tokens=1-2" %%A in ("!rnd! !oppos!") do ( set str1=!samp:~-%%A! set str2=!samp:~0,%%B! ) set samp=!str2!%put2%!str1! set /a "j+=1","i+=1" goto :add ) goto :EOF
- /Generate strings of brackets.
- Check for Balance...
- Uses Markov Algorithm.
- checkforbalance
set "changes=!samp!"
- check_loop
if "!changes!"=="" goto itsbal if "!input!"=="!changes!" goto notbal
set input=!changes! set "changes=!input:[]=!" goto check_loop
- itsbal
echo. echo %samp% is Balanced. goto :EOF
- notbal
echo. echo %samp% is NOT Balanced. goto :EOF
- /Check for Balance.</lang>
- Output:
[][][[]][][]]][][][[ is NOT Balanced. [[[[[]][[]][]][][]]] is Balanced. [[[[[]]]]][][][]][][ is NOT Balanced. ][[[[[[[]]][]]][][]] is NOT Balanced. [][[[[]]]][[[[]]]][] is Balanced. [[[][[[]][][]]]][][] is Balanced. [[][[]][[]]]]][][[[] is NOT Balanced. [][][]][][]]][][][[[ is NOT Balanced. [[]][][][[][[[]]]][] is Balanced. [[[[[][[][[]]]]][]]] is 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
\ $
^ < <$<</lang>
Bracmat
Bracmat has no 'random' function, so the shuffle is a bit improvised. A variable someNumber is initialised with a big number is repeatedly divided by the number of '['s in the test string until zero. The remainders are used as index to partition and swap the first half of the test string. Then the second half and first half are also swapped. The test whether the test string is balanced is simple, but not very efficient.
<lang bracmat>( (bal=|"[" !bal "]" !bal)
& ( generate
= a j m n z N S someNumber
. !arg:<1&
| 11^123+13^666+17^321:?someNumber
& (!arg:?n)+1:?N
& :?S
& whl
' (!n+-1:~<0:?n&"[" "]" !S:?S)
& whl
' ( !someNumber:>0
& mod$(!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>
Output:
user> (->> (range 10)
(map gen-brackets ,)
(map (juxt identity balanced?) ,) vec)
[["" true]
["[]" true]
["[[]]" true]
["[][[]]" true]
["[]][][][" nil]
["[[[[[]]]]]" true]
["]][[][][[[]]" nil]
["[]]]][[[[]][][" nil]
["][][[]]][[][][][" nil]
["][][]]][]][[[][[[]" nil]
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 ((result (make-string (* 2 n)))
(opening n)
(closing n))
(dotimes (i (* 2 n) result)
(setf (aref result 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
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
<lang elena>#define system.
- define system'routines.
- define extensions.
- symbol randomBrackets =
{
new : aLength
= (0 == aLength)
? [ emptyLiteralValue ]
! [
#var aBrackets :=
Array new &length:(aLength int) set &every: (&index:i) [ #91 ]
+
Array new &length:(aLength int) set &every: (&index:i)[ #93 ].
aBrackets randomize:(aLength * 2).
^ aBrackets summarize:(String new) literal.
].
}.
- class(extension)op
{
#method isBalanced
[
#var aCounter := Integer new:0.
self seek &each:aChar [ (aCounter += (aChar => #91 ? [ 1 ] #93 ? [ -1 ])) < 0 ].
^ (0 == aCounter).
]
}
- symbol program =
[
0 to:9 &doEach: (:aLength)
[
#var anStr := randomBrackets new:aLength.
console writeLine:"""":anStr:"""":((anStr isBalanced) => true ? [ " is balanced" ] false ? [ " 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 ->
string = generate(n)
result = is_balanced(string) |> task_balanced
IO.puts "#{string} is #{result}"
end)
end
def generate( 0 ), do: []
def generate( n ) do
for _ <- 1..2*n, do: generate_bracket(:rand.uniform(2))
end
defp generate_bracket( 1 ), do: "["
defp generate_bracket( 2 ), do: "]"
def is_balanced( string ), do: is_balanced_loop( string, 0 )
defp is_balanced_loop( _string, 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
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>
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>
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
<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 s = printf "Good \"%s\"\n" s
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 "]]][[[][][][[][]]["
^
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 Brackets {
public static boolean checkBrackets(String str){
int mismatchedBrackets = 0;
for(char ch:str.toCharArray()){
if(ch == '['){
mismatchedBrackets++;
}else if(ch == ']'){
mismatchedBrackets--;
}else{
return false; //non-bracket chars
}
if(mismatchedBrackets < 0){ //close bracket before open bracket
return false;
}
}
return mismatchedBrackets == 0;
}
public static String generate(int n){
if(n % 2 == 1){ //if n is odd we can't match brackets
return null;
}
String ans = "";
int openBracketsLeft = n / 2;
int unclosed = 0;
while(ans.length() < n){
if(Math.random() >= .5 && openBracketsLeft > 0 || unclosed == 0){
ans += '[';
openBracketsLeft--;
unclosed++;
}else{
ans += ']';
unclosed--;
}
}
return ans;
}
public static void main(String[] args){
String[] tests = {"", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"};
for(int i = 0; i <= 16; i+=2){
String bracks = generate(i);
System.out.println(bracks + ": " + checkBrackets(bracks));
}
for(String test: tests){
System.out.println(test + ": " + checkBrackets(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
JavaScript
<lang javascript> function createRandomBracketSequence(maxlen) {
var chars = { '0' : '[' , '1' : ']' };
function getRandomInteger(to)
{
return Math.floor(Math.random() * (to+1));
}
var n = getRandomInteger(maxlen);
var result = [];
for(var i = 0; i < n; i++)
{
result.push(chars[getRandomInteger(1)]);
}
return result.join("");
}
function bracketsAreBalanced(s) {
var open = (arguments.length > 1) ? arguments[1] : '[';
var close = (arguments.length > 2) ? arguments[2] : ']';
var c = 0;
for(var i = 0; i < s.length; i++)
{
var ch = s.charAt(i);
if ( ch == open )
{
c++;
}
else if ( ch == close )
{
c--;
if ( c < 0 ) return false;
}
}
return c == 0;
}
var c = 0; while ( c < 5 ) {
var seq = createRandomBracketSequence(8); alert(seq + ':\t' + bracketsAreBalanced(seq)); c++;
} </lang> Output:
: true [[]: false ]][[[][]: false ]]: false [][[]]: true
Recursively remove occurrences of '[]':
<lang javascript>
function checkBalance(i) {
while (i.length % 2 == 0) {
j = i.replace('{}',);
if (j == i)
break;
i = j;
}
return (i?false:true);
}
var g = 10; while (g--) {
var N = 10 - Math.floor(g/2), n=N, o=;
while (n || N) {
if (N == 0 || n == 0) {
o+=Array(++N).join('}') + Array(++n).join('{');
break;
}
if (Math.round(Math.random()) == 1) {
o+='}';
N--;
}
else {
o+='{';
n--;
}
}
alert(o+": "+checkBalance(o));
} </lang>
Julia
<lang Julia>function balanced(str)
i = 0 for c in str if c == '[' i +=1 elseif c == ']' i -=1 end if i < 0 return false end end i == 0 ? true : false
end
brackets(n) = join(shuffle([("[]"^n)...]))
map(x -> (x, balanced(x)), [brackets(i) for i = 0:8]) </lang>
- Output:
("",true)
("][",false)
("][[]",false)
("[[][]]",true)
("]][[[]][",false)
("[[]]][[][]",false)
("[[][[]][]][]",true)
("]]][][[[][][[]",false)
("[[[[[][]]]]]][[]",false)
Starting with Julia v0.3, a foldl function is available, so that balanced may be written shortly (but not as efficiently) as follows: <lang Julia>balanced(str) = foldl((x,y)->x<0? -1: x+y, 0, [(x=='[')-(x==']') for x=str])==0</lang>
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
<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>
Nim
<lang nim>import math randomize()
proc shuffle(s: var string) =
for i in countdown(s.high, 0): swap(s[i], s[random(s.len)])
proc gen(n): string =
result = newString(2 * n) for i in 0 .. <n: result[i] = '[' for i in n .. <(2*n): result[i] = ']' shuffle(result)
proc balanced(txt): 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
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 ==
}
func: 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>
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;
}
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($s) ?? "is" !! "is not" } well-balanced";</lang>
Phix
<lang Phix>function check_brackets(sequence s) integer level = 0
for i=1 to length(s) do
switch s[i]
case '[': level += 1
case ']': level -= 1
if level<0 then exit end if
end switch
end for
return (level=0)
end function
sequence s constant ok = {"not ok","ok"}
for i=1 to 10 do
for j=1 to 2 do
s = shuffle(join(repeat("[]",i-1),""))
printf(1,"%s %s\n",{s,ok[check_brackets(s)+1]})
end for
end for</lang>
- Output:
ok ok [] ok ][ not ok [][] ok ][][ not ok []][][ not ok ][][[] not ok ][[][]][ not ok [][[][]] ok []]][[[]][ not ok ][]][[[]][ not ok ][[]]]][[][[ not ok [][[]][[]][] ok []][][]]][[[[] not ok [[][][]][][[]] ok [[][]][][[]][[]] ok ][][[[[][]]][]][ not ok [[[[]]][][[[][]]]] ok [[[]]][[[[][]]][]] ok
PHP
The sample is given as unix shell script, you need to have php-cli (or what your package manager calls it) installed.
<lang PHP>#!/usr/bin/php <?php
- brackets generator
function bgenerate ($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
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 '][[][[[[[]'
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
<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</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>
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(permute(c(rep('[',n),rep(']',n))),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>
REXX
with examples + 40 permutations
<lang rexx>/*REXX program checks for balanced (square) brackets [ ] */ @.=0; yesNo.0=left(,40) 'unbalanced' /*forty +1 leading blanks.*/
yesNo.1= 'balanced'
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 q= ']]][[[[]' ; call checkBal q; say yesNo.result q
do j=1 for 40
q=translate(rand(random(1, 8)), '[]', 01)
call checkBal q; if result==-1 then iterate /*skip if duplicated.*/
say yesNo.result q /*display the result.*/
end /*j*/ /* [↑] generate 40 random "Q" strings.*/
exit /*stick a fork in it, we're all done. */ /*────────────────────────────────────────────────────────────────────────────*/ ?: ?=random(0,1); return ? || \? /*────────────────────────────────────────────────────────────────────────────*/ rand: ??=copies(?()?(), arg(1)); _=random(2, length(??))
return left(??, _-1)substr(??, _)
/*────────────────────────────────────────────────────────────────────────────*/ checkBal: procedure expose @.; parse arg y /*get the "bracket" expression. */
if @.y then return -1 /*already done this expression ? */
@.y=1 /*indicate expression processed. */
!=0; do j=1 for length(y); _=substr(y,j,1) /*get a char.*/
if _=='[' then !=!+1 /*bump nest #*/
else do; !=!-1; if !<0 then return 0; end
end /*j*/
return !==0 /* [↑] "!" is the nested counter.*/</lang>
output (not repeatable due to the use of the random BIF:
balanced
balanced [][][][[]]
unbalanced [][][][[]]][
unbalanced [
unbalanced ]
balanced []
unbalanced ][
unbalanced ][][
balanced [[]]
balanced [[[[[[[]]]]]]]
unbalanced [[[[[]]]][]
balanced [][]
unbalanced []][[]
unbalanced ]]][[[[]
unbalanced ][[]][[]
unbalanced ][[]][[]][[]][[]][[]][[]][[]
unbalanced ][][][][][][][][][][
unbalanced ][[]][[]][[]][[]
unbalanced ][][][][][][][][][][][][][][
unbalanced ][[]][[]][[]
unbalanced []][[]][[]][
unbalanced []][[]][[]][[]][[]][[]][[]][
unbalanced []][
unbalanced ][][][][][][
unbalanced []][[]][[]][[]][[]][[]][
unbalanced ][][][][][][][][
balanced [][][][][][]
balanced [][][][][][][][]
unbalanced []][[]][[]][[]][
unbalanced []][[]][[]][[]][[]][
balanced [][][][][][][][][][][][]
balanced [][][][][][][][][][][][][][]
unbalanced []][[]][
unbalanced ][[]][[]][[]][[]][[]][[]
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>
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 (brackets) 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.
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 numerous generated balanced (square) brackets [ ] */
bals=0
- =0; do j=1 until length(q)>20 /*generate lots of bracket permutations*/
q=translate(strip(x2b(d2x(j)),'L',0),"][",01) /*convert ──► []*/
if countStr(']',q)\==countstr('[',q) then iterate /*is compliant? */
call checkBal q
end /*j*/ /*have all 20─character possibilities? */
say say # " expressions were checked, " bals ' were balanced, ' ,
#-bals " were unbalanced."
exit /*stick a fork in it, we're all done. */ /*────────────────────────────────────────────────────────────────────────────*/ checkBal: procedure expose # bals; parse arg y; #=#+1 /*bump count.*/ !=0
do j=1 for length(y)
if substr(y,j,1)=='[' then !=!+1
else do; !=!-1; if !<0 then leave; end
end /*j*/
bals=bals + (!==0) return !==0 /*────────────────────────────────────────────────────────────────────────────*/ 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:
125477 expressions were checked, 23713 were balanced, 101764 were unbalanced.
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>
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 ((and (null? chars) (= 0 sum))
#t)
((null? chars)
#f)
((char=? #\[ (car chars))
(b (cdr chars) (+ sum 1)))
((= sum 0)
#f)
(else
(b (cdr chars) (- sum 1)))))
(b (string->list string) 0))
(balanced-brackets "")
(balanced-brackets "[]") (balanced-brackets "[][]") (balanced-brackets "[[][]]")
(balanced-brackets "][") (balanced-brackets "][][") (balanced-brackets "[]][[]") </lang>
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;
}
[']','[','[[]','][]','[[]]','[[]]]][][]]','x[ y [ [] z ]][ 1 ][]abcd'].each { |str|
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
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).
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 shuffle (list)
(for* ((vec (vector-list list))
(len (length vec))
(i 0))
((< i len) (list-vector vec))
((inc i))
(let ((j (random r len))
(temp [vec i]))
(set [vec i] [vec j])
(set [vec j] temp))))
(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.
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>
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
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