將兩個有序連結串列合併為一個新的有序連結串列並返回。新連結串列是通過拼接給定的兩個連結串列的所有節點組成的。 

示例：

輸入：1->2->4, 1->3->4
輸出：1->1->2->3->4->4

class Solution {
	public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
		ListNode next = new ListNode(0);
		

		if (null == l1) {
			return l2;
		}

		if (null == l2) {
			return l1;
		}

		ListNode result =next;
		
		while (null != l1 || null != l2) {

			if (null == l1) {
				next.next = l2;
				break;
			}
			if (null == l2) {
				next.next = l1;
				break;
			}
			if (l1.val > l2.val) {
				next.next = l2;
				l2 = l2.next;
			} else {
				next.next = l1;
				l1 = l1.next;
			}
			next = next.next;
		}

		return result.next;
	}
}