LeetCode 21. Merge Two Sorted Lists （合并两个有序链表）

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.

题目标签：Linked List

　　题目给了我们两个lists，让我们有序的合并两个 lists。

　　这题利用递归可以从list 的最后开始向前链接nodes，代码很简洁，清楚。

Java Solution:

Runtime beats 74.35%

完成日期： 06/09/2017

关键词：singly-linked list

关键点：利用递归从最后开始链接nodes

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 class Solution 
10 {
11     public ListNode mergeTwoLists(ListNode l1, ListNode l2) 
12     {
13         if(l1 == null)
14             return l2;
15         if(l2 == null)
16             return l1;
17         
18         if(l1.val < l2.val)
19         {
20             l1.next = mergeTwoLists(l1.next, l2);
21             return l1;
22         }
23         else
24         {
25             l2.next = mergeTwoLists(l1, l2.next);
26             return l2;
27         }
28     }
29     
30 }

参考资料：

https://discuss.leetcode.com/topic/45002/java-1-ms-4-lines-codes-using-recursion

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