题目地址

https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/

题目描述

19. Remove Nth Node From End of List

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Follow up: Could you do this in one pass?

 

Example 1:


Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]
Example 2:

Input: head = [1], n = 1
Output: []
Example 3:

Input: head = [1,2], n = 1
Output: [1]

思路

通常这种题, 需要做个dummy.
快慢指针问题.
快指针先走n步. 然后快慢一起走, 当快指针走到尽头后, 在慢指针处进行删除.
最后return dummy.next.

关键点

代码

语言支持：Java

/**
 * 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) {
        if (head == null || n <= 0) {
            return head;
        }
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        for (int i = 0; i < n; i++) {
            if (head == null) {
                return null;
            }
            head = head.next;
        }
        ListNode preDelete = dummy;
        while(head != null) {
            preDelete = preDelete.next;
            head = head.next;
        }
        preDelete.next = preDelete.next.next;
        
        return dummy.next;
    }
}