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.
tag : dummy node . 类似题： reverse linked list
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode swapPairs(ListNode head) {
ListNode dummy = new ListNode(0);
dummy.next = head;
head = dummy;
while(head.next != null && head.next.next != null){
ListNode n1 = head.next;
ListNode n2 = head.next.next;
head.next = n2;
n1.next = n2.next;
n2.next = n1;
head = n1;
}
return dummy.next;
}
}
leetcode : Swap nodes in pairs
原文：http://www.cnblogs.com/superzhaochao/p/6400741.html