Given a linked list, swap every two adjacent nodes and return its head.
For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.
Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.
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 swapPairs(ListNode head) {
11
12 if(head==null||head.next==null)
13 return head;
14 ListNode first=head;
15 ListNode second=first.next;
16 ListNode temp=first;
17 head=second;
18
19 while(first!=null&&second!=null)
20 {
21 temp.next=second;
22 first.next=second.next;
23 temp=first;
24 second.next=first;
25 first=first.next;
26 if(first!=null&&first.next!=null)
27 {
28 second=first.next;
29 }
30 else break;
31 }
32 return head;
33 }
34
35 }
