Swap Nodes in Pairs

题目描述

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.

题目解答

解题思路

该题是Reverse Nodes in K-group 特殊情况， 首先应该引入头结点，来统一化节点的操作， 用来三个节点指针(pre, first, second)来控制节点的翻转。

代码实现

public class Solution {
public ListNode swapPairs(ListNode head) {
if(head == null)
return null;
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode pre = dummy;
ListNode first = pre.next;
ListNode second = first.next;
while (second != null){
//实现翻转
first.next = second.next;
second.next = pre.next;
pre.next = second;

pre =  first;
first = pre.next;
if(first == null)
break;
second = first.next;
}
return dummy.next;

}
}