balanced-parens.js

var paren = function(n)
{
	var arr = [],
		decodeParens = function(code, len)
		{
			for (var i=0; i<len; ++i)
				var open = (((code & (0x1 << i)) >> i) ? '(' : ')') + (open || '');
			return open;
		};

	(function compute(len, sofar, bits, unbalanced) {

		// we are done
		if (!len && !unbalanced)
			arr.push(decodeParens(sofar));

		// open one more '(' if we aren't done yet
		if (len)
			compute(len-1, (sofar << 1) | 0x1, bits+1, unbalanced+1);

		// we have an unbalanced paren... close it
		if (unbalanced)
		{
			// console.log('unbalanced', unbalanced);
			compute(len, (sofar << 1) | 0x0, bits+1, unbalanced-1);
		}

	})(n, 0, 0, 0);
	return arr;
};