Balanced brackets

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

This example is incomplete. Strings are not generated. Please ensure that it meets all task requirements and remove this message.

<lang d>import std.stdio, std.algorithm, std.string;

void main() {

 foreach (s; ",[],[][],[[][]],][,][][,[]][[]".split(","))
   writefln("%-8s 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

This example is incomplete. Strings are not generated. Please ensure that it meets all task requirements and remove this message.

<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>

Tcl

This example is incomplete. Strings are not generated. Please ensure that it meets all task requirements and remove this message.

<lang tcl>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}

}</lang> Demonstration code: <lang tcl>foreach s {"" "[]" "][" "[][]" "][][" "[[][]]" "[]][[]"} {

   puts "$s\t-> [expr {[balanced $s] ? {OK} : {NOT OK}}]"

}</lang> Output:

	-> OK
[]	-> OK
][	-> NOT OK
[][]	-> OK
][][	-> NOT OK
[[][]]	-> OK
[]][[]	-> NOT OK

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>