Leetcode21.Merge Two Sorted Lists

题目描述

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

思路

思路：两个指着（程序中直接使用ListNode）如果当前l1的value大于l2的value则将l2的值赋给result，
然后递归比较l1和l2.next。如果当前l1的value小于l2的value则将l1的值赋给result，然后递归比较l2和l1.next。

代码

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1==null)
            return l2;
        if(l2==null)
            return l1;
        ListNode result;
         if(l1.val<l2.val){
             result=l1;
             result.next=mergeTwoLists(l1.next,l2);
         }else{
             result = l2;
             result.next = mergeTwoLists(l1,l2.next);
         }
        return result;
    }
}