Task:

 Generate a string with   N   opening brackets   [   and with   N   closing brackets   ],   in some arbitrary order. 
 Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.


Examples

   (empty)      OK
   []           OK   
   [][]         OK   
   [[][]]       OK 
   ][         NOT OK
   ][][       NOT OK
   []][[]     NOT OK



#!/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)
}
 