js: maximum sub array solution using divide and conquer

submax.js

// O(n log n)
Array.prototype.submax = function() {

	if(this.length === 0) return 0;
	if(this.length === 1) return this[0];

	var m = Math.floor(this.length / 2);
	
	var max_left	= find_max(this, m - 1, 0);
	var max_right 	= find_max(this, m, this.length);

	function find_max(a, s, e) {
		var max = sum = 0;
		for(var i = s; s < e ? i < e : i >= e; s < e ? i++ : i--) {
			sum += a[i];
			max = Math.max(max, sum);
		}
		return max;
	}

	var center 	= max_left + max_right;
	var left 	= this.slice(0, m).submax()
	var right 	= this.slice(m).submax()

	return Math.max(left, center, right);

}