Merge Two Sorted Lists 解答

Question

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.

Solution

The key to the solution here is to create a new linked list by creating a fake head.

 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 public class Solution {
10     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
11         if (l2 == null)
12             return l1;
13         if (l1 == null)
14             return l2;
15         ListNode fakeHead = new ListNode(0);
16         ListNode tmp = fakeHead;
17         ListNode p1 = l1, p2 = l2;
18         while (p1 != null && p2 != null) {
19             if (p1.val < p2.val) {
20                 tmp.next = p1;
21                 p1 = p1.next;
22             } else {
23                 tmp.next = p2;
24                 p2 = p2.next;
25                 
26             }
27             tmp = tmp.next;
28         }
29         while (p1 != null) {
30             tmp.next = p1;
31             tmp = tmp.next;
32             p1 = p1.next;
33         }
34         while (p2 != null) {
35             tmp.next = p2;
36             tmp = tmp.next;
37             p2 = p2.next;
38         }
39         return fakeHead.next;
40     }
41 }