143.重排链表。双百0ms，简单易懂双指针

Split_token

于 2022-01-18 00:46:00 发布

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分类专栏： LeetCode 文章标签：链表数据结构

本文链接：https://blog.youkuaiyun.com/Split_token/article/details/122551797

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本文介绍了一种链表操作的方法，包括寻找链表中点、翻转链表后半部分及重新连接链表节点等步骤，实现了链表的有序重组。

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找中点，后半段逆转，然后一前一后依次连接

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null) return null;
        ListNode tail = head;
        head = head.next;

        tail.next = null;

        while (head != null) {
            ListNode temp = head.next;
            head.next = tail;
            tail = head;
            head = temp;
        }
        return tail;
    }

    public void reorderList(ListNode head) {
        if (head == null || head.next == null || head.next.next == null) return;
        //找中点，链表分成两个
        ListNode slow = head, fast = head;
        while (fast.next != null && fast.next.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }
        // 翻转
        ListNode newHead = slow.next;
        slow.next = null;
        newHead = reverseList(newHead);
    
        // 依次连接
        while (newHead != null) {
            ListNode temp = newHead.next;
            newHead.next = head.next;
            head.next = newHead;
            head = newHead.next;
            newHead = temp;
        }
    }
}