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



 
grammar balancedBrackets ;
 
options {
	language = Java;
}
 
bb	:	{System.out.print("input is: ");} (balancedBrackets {System.out.print($balancedBrackets.text);})* NEWLINE {System.out.println();}
	;
balancedBrackets
	:	OpenBracket balancedBrackets* CloseBracket
	;
OpenBracket
	:	'['
	;
CloseBracket
	:	']'
	;
NEWLINE	:	'\r'? '\n'
	;
 