Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

list順序合併就可以了

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 
 
*/
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode res = new ListNode(0);
        ListNode l3 = res;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                l3.next = l1;
                l3 = l3.next;
                l1 
 
= l1.next;
            } else {
                l3.next = l2;
                l3 = l3.next;
                l2 = l2.next;
            }
        }
        if (l1 == null) {
            l3.next = l2;
        } else {
            l3.next = l1;
        }
        return res.next;
    }
}