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 $N
closing brackets ("]"
), in some arbitrary order. Determine whether the string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.
Examples:
(empty) OK [] OK ][ NOT OK [][] OK ][][ NOT OK [[][]] OK []][[] NOT OK
D
<lang d>import std.stdio, std.algorithm, std.string;
void main() {
foreach (s; ",[],[][],[[][]],][,][][,[]][[]".split(",")) writefln("%s is%s balanced", s, s.balancedParens('[', ']') ? "" : " not");
}</lang> Output:
is balanced [] is balanced [][] is balanced [[][]] is balanced ][ is not balanced ][][ is not balanced []][[] is not balanced
Perl 6
<lang perl6>sub balanced($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 gen(N): ... txt = ['['] * N + [']'] * 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 ("%r is%s balanced" % (txt, if balanced(txt) else ' not')) ... 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 '[[[[[][[[]][]]]]]]' is balanced</lang>