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.

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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

/**
 * 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) 
    {
        if(l1 == null)
            return l2;
        if(l2 == null)
            return l1;
        
        if(l1.val < l2.val)
        {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }
        else
        {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }
    
}

参考资料：

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

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题目来源：https://leetcode.com/