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.
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 swapPairs(ListNode head) { 14 if (head==null || head.next==null) return head; 15 ListNode preHead = new ListNode(0); 16 preHead.next = head; 17 ListNode pre = preHead; 18 ListNode cur = head; 19 20 while (cur!=null && cur.next!=null){ 21 ListNode temp = cur.next.next; 22 pre.next = cur.next; 23 cur.next.next = cur; 24 cur.next = temp; 25 pre=cur; 26 cur = cur.next; 27 } 28 29 return preHead.next; 30 } 31 }
原文：http://www.cnblogs.com/lishiblog/p/4111921.html