Leetcode#21 Merge Two Sorted Lists

Posted on | In
leetcode solutions (through java)

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

Solution:

递归

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
/**
 * 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;
        ListNode result=null;
        if(l1.val<l2.val){
            result=l1;
            result.next=mergeTwoLists(l1.next,l2);   
        }else{
            result=l2;
            result.next=mergeTwoLists(l1,l2.next); 
        }
        return result;
    }
}
// Time Complexity: O(n + m)
// Space complexity : O(n + m)