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



func balanced (str) {
 
    var depth = 0
    str.each { |c|
           if(c=='['){ ++depth }
        elsif(c==']'){ --depth < 0 && return false }
    }
 
    return !depth
}
 
for str [']','[','[[]','][]','[[]]','[[]]]][][]]','x[ y [ [] z ]][ 1 ][]abcd'] {
    printf("%sbalanced\t: %s\n", balanced(str) ? "" : "NOT ", str)
}