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leetcode 24

admin 11月 13, 2020 0

LeetCode 24.Swap Nodes in Pairs

题目

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

Example

1	Given 1->2->3->4, you should return the list as 2->1->4->3.

Note:

Your algorithm should use only constant extra space.
You may not modify the values in the list’s nodes, only nodes itself may be changed.

解题思路：

以Example为例：

JAVA代码

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        if(head == null || head.next==null  )
            return head;
        ListNode temp1=head.next;
        head.next=temp1.next;
        temp1.next=head;
        head=temp1;
        temp1=head.next;
        while(temp1.next!=null && temp1.next.next!=null){
            ListNode temp2=temp1.next;
            temp1.next=temp2.next;
            temp2.next=temp1.next.next;
            temp1.next.next=temp2;
            temp1=temp2;
        }
        return head;
    }
}