技術標籤：LeetCode-300leetcode

題目地址：

中文：https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/
英文：https://leetcode.com/problems/remove-nth-node-from-end-of-list/

題目描述：

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]

Constraints:

The number of nodes in the list is sz.
1 <= sz <= 30
0 <= Node.val <= 100
1 <= n <= sz

思路：

本題目要將倒數第n個結點從連結串列中刪除，然後返回頭結點。

題解：

/**
 * 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) {
        //頭部加個頭結點，統一操作，否則被刪的是第一個結點會很麻煩
        ListNode res = new ListNode(0);
        res.next = head;
        ListNode first = res;
        ListNode second = res;
        //把後邊的指標往後挪
        for(int i=0;i<n;i++){
            second = second.next;
        }

        while (second.next!=null){
            first = first.next;
            second = second.next;
        }

        first.next = first.next.next;

        return res.next;
    }
}