21. Merge Two Sorted Lists

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.

代碼如下:

 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(l1==null&&l2==null)
12         return null;
13         if(l1==null&&l2!=null)
14         return l2;
15         if(l1!=null&&l2==null)
16         return l1;
17         
18         ListNode head=l1.val<=l2.val?l1:l2;
19         ListNode p=head;
20         if(head==l1)
21         l1=l1.next;
22         else if(head==l2)
23         l2=l2.next;
24         
25         while(l1!=null&&l2!=null)
26         {
27             head.next=l1.val<=l2.val?l1:l2;
28         if(head.next==l1)
29         l1=l1.next;
30         else if(head.next==l2)
31         l2=l2.next;
32         head=head.next;
33         }
34         
35         if(l1==null&&l2==null)
36         head.next=null;
37         if(l2!=null)
38         head.next=l2;
39         if(l1!=null)
40         head.next=l1;
41         
42         return p;
43     }
44 }