两个有序链表连接（归并排序中用到的）

刚才写了k个，顺手写个2个的，在链表的归并排序中很有用，效率非常好

 1 /**

 2  * Definition for singly-linked list.

 3  * public class ListNode {

 4  *     int val;

 5  *     ListNode next;

 6  *     ListNode(int x) {

 7  *         val = x;

 8  *         next = null;

 9  *     }

10  * }

11  */

12 public class Solution {

13     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

14         

15         if(l1==null&&l2==null) return null;

16         if(l1==null) return l2;

17         if(l2==null) return l1;

18         

19         ListNode head=new ListNode(-2);

20         ListNode tail=head;

21         while(l1!=null&&l2!=null)

22         {

23             if(l1.val>l2.val)

24             {

25                 tail.next=l2;

26                 tail=tail.next;

27                 l2=l2.next;

28             }

29             else

30             {

31                 tail.next=l1;

32                 tail=tail.next;

33                 l1=l1.next;

34             }

35         }

36         if(l1!=null) tail.next=l1;

37         if(l2!=null) tail.next=l2;

38         return head.next;

39             

40         }

41         

42         

43   

44 }

View Code