Balanced brackets
You are encouraged to solve this task according to the task description, using any language you may know.
Problem: Generate a string with $N opening brackets ("[") and $N closing brackets ("]"), in some arbitrary order. Determine whether the string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.
Examples:
(empty) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK
Perl 6
<lang perl6>sub balanced($s) {
my $l = 0;
for $s.comb {
when "]" {
--$l;
return False if $l < 0;
}
when "[" {
++$l;
}
}
return $l == 0;
}
my $N = get; my $s = (<[ ]> xx $N).pick(*).join; say "$s {balanced($s) ?? "is" !! "is not"} well-balanced"</lang>
PureBasic
<lang PureBasic>Procedure Balanced(String$)
Protected *p.Character, cnt
*p=@String$
While *p\c
If *p\c='['
cnt+1
ElseIf *p\c=']'
cnt-1
EndIf
If cnt<0: Break: EndIf
*p+SizeOf(Character)
Wend
If cnt=0
ProcedureReturn #True
EndIf
EndProcedure</lang> Testing the procedure <lang PureBasic>Debug Balanced("") ; #true Debug Balanced("[]") ; #true Debug Balanced("][") ; #false Debug Balanced("[][]") ; #true Debug Balanced("][][") ; #false Debug Balanced("[[][]]") ; #true Debug Balanced("[]][[]") ; #false</lang>
Python
<lang python>>>> def balanced(txt): ... braced = 0 ... for ch in txt: ... if ch == '[': braced += 1 ... if ch == ']': ... braced -= 1 ... if braced < 0: return False ... return True ... >>> for txt in ',[],[][],[[][]],][,][][,[]][[]'.split(','): ... print ("%r is%s balanced" % (txt, if balanced(txt) else ' not')) ... is balanced '[]' is balanced '[][]' is balanced '[[][]]' is balanced '][' is not balanced '][][' is not balanced '[]][[]' is not balanced</lang>