1. class Solution {
    2.     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    3.         if(l1 == null){
    4.             return l2;
    5.         }
    6.         if(l2 == null){
    7.             return l1;
    8.         }
    9.         ListNode head = null;
    10.         ListNode tmp = null;
    12.         if(l1.val <= l2.val){
    13.             tmp = l1;
    14.             head = l1;
    15.             l1 = l1.next;
    16.         } else {
    17.             tmp = l2;
    18.             head = l2;
    19.             l2 = l2.next;
    20.         }
    22.         while(l1!=null && l2!=null){
    23.             if(l1.val <= l2.val){
    24.                 tmp.next = l1;
    25.                 l1 = l1.next;
    26.             } else {
    27.                 tmp.next = l2;
    28.                 l2 = l2.next;
    29.             }
    30.             tmp = tmp.next;
    31.             tmp.next = null;
    32.         }
    33.         if(l1 != null){
    34.             tmp.next = l1;
    35.         }
    36.         if(l2 != null){
    37.             tmp.next = l2;
    38.         }
    39.         return head;
    40.     }
    41. }