swap-nodes-in-pairs(单链表交换点对)

题目描述

Given a linked list, swap every two adjacent nodes and return its head.

For example,

Given1->2->3->4, you should return the list as2->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.

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) {
*         val = x;
*         next = null;
*     }
* }
*/
public class Solution {
public ListNode swapPairs(ListNode head) {
ListNode node = new ListNode(0);
node.next = head;
ListNode p = node;
ListNode tmp;
while(p.next != null && p.next.next != null) {
tmp = p.next.next;
p.next.next = tmp.next;
tmp.next = p.next;
p.next = tmp;
p = tmp.next;
}
head = node.next;
node.next = null;
return head;
}
}