题目描述

给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。

示例 1：

img

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输入：head = [1,2,3,4,5], n = 2
输出：[1,2,3,5]

示例 2：

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输入：head = [1], n = 1
输出：[]

示例 3：

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输入：head = [1,2], n = 1
输出：[1]

提示：

  • 链表中结点的数目为 sz
  • 1 <= sz <= 30
  • 0 <= Node.val <= 100
  • 1 <= n <= sz

题目思路

  • 双指标

Java

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import javax.swing.*;
import java.util.List;

/**
 * Definition for singly-linked list.
 * public class ListNode {
 * int val;
 * ListNode next;
 * ListNode() {}
 * ListNode(int val) { this.val = val; }
 * ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode start = head;
        ListNode end = head;
        if (head.next == null && n == 1) {
            return null;
        }
        int i = 0;
        for (; i < n; i++) {
            if (end != null) {
                end = end.next;
            }
        }
        if (end == null) {
            if (n - i > 1) {
                return start;
            }
            return start.next;
        }
        while (end.next != null) {
            start = start.next;
            end = end.next;
        }
        start.next = start.next.next;
        return head;
    }
}