21. 合并两个有序链表

输入：l1 = [1,2,4], l2 = [1,3,4]
输出：[1,1,2,3,4,4]

  1. /**
  2.  * Definition for singly-linked list.
  3.  * public class ListNode {
  4.  *     int val;
  5.  *     ListNode next;
  6.  *     ListNode() {}
  7.  *     ListNode(int val) { this.val = val; }
  8.  *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  9.  * }
  10.  */
  11. class Solution {
  12.     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
  13.         if (l1 == null) {
  14.             return l2;
  15.         } else if (l2 == null) {
  16.             return l1;
  17.         } else if (l1.val < l2.val) {
  18.             l1.next = mergeTwoLists(l1.next, l2);
  19.             return l1;
  20.         } else {
  21.             l2.next = mergeTwoLists(l1, l2.next);
  22.             return l2;
  23.         }
  25.     }
  27. //作者：LeetCode-Solution
  28. //链接：https://leetcode-cn.com/problems/merge-two-sorted-lists/solution/he-bing-liang-ge-you-xu-lian-biao-by-leetcode-solu/
  30. }