public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
		ListNode temp = new ListNode(-1);
		ListNode res = temp;
		while (l1 != null && l2 != null) {
			if (l1.val < l2.val) {
				temp.next = l1;
				l1 = l1.next;
				temp = temp.next;
			} else {
				temp.next = l2;
				l2 = l2.next;
				temp = temp.next;
			}
		}
		if (l1 != null) {
			temp.next = l1;
		}
		if (l2 != null)
			temp.next = l2;
		return res.next;
	}