leetcode [#24]

目录

• 1. 题目
• 2. 解决方案
• 3. 注意事项

题目

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

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

Note:
Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

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解决方案

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

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注意事项

1. 默认链表有偶数个元素。
2. 遍历整个链表，每两个做交换即可。