列表重新排序——Leetcode系列（八）

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原创最新推荐文章于 2026-04-14 09:48:45 发布 893 阅读 AI 写同款· GEO 优化 ›

LeetCode力扣-hot100系列（1）虽然开始写力扣系列的文章的时候，我的hot100题已经刷了71道了，以及代码随想录上面的题也跟着刷。并且之前也做了大量的笔记，包含差不多5000行~8000行左右（还包含左神的数据结构中的题目）。为什么我只给了一个范围呢？因为一不小心把vscode中的整个工作区删了，并且一并连回收站也清理了。当我意识到这里面还有我的笔记的时候，我已经删干净了，连同我做完的一个项目（还没来得及放在gitee上）。上面的案例告诉我们一定要做备份！！！阅读详情

Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You must do this in-place without altering the nodes' values.

For example,
Given {1,2,3,4}, reorder it to {1,4,2,3}.

My Answer

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public void reorderList(ListNode head) {
        if(head == null || head.next == null){
            return;
        }
        int total = 0;
        ListNode pivot = head;
        //count the number of nodes in the list
        while(pivot != null){
            pivot = pivot.next;
            total++;
        }
        int splitIndex = total / 2 + total % 2;
        pivot = head;
        int shiftTime = 0;
        //get the middle node in the list
        while(shiftTime < splitIndex){
            pivot = pivot.next;
            shiftTime++;
        }
        ListNode secondHead = pivot;
        pivot = pivot.next;
        secondHead.next = null;
        //reverse the second half of the list
        while(pivot != null){
            ListNode temp = pivot;
            pivot = pivot.next;
            temp.next = secondHead;
            secondHead = temp;
        }
        ListNode firstPivot = head;
        ListNode secondPivot = secondHead;
        //get the node from the first half and second half of the list one by one
        while(secondPivot != null){
            ListNode temp = secondPivot;
            secondPivot = secondPivot.next;
            temp.next = firstPivot.next;
            firstPivot.next = temp;
            firstPivot = temp.next;
        }
        if(firstPivot != null){
            firstPivot.next = null;
        }
    }
}

题目来源：https://oj.leetcode.com/problems/reorder-list/

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