题解 | #删除链表的倒数第n个节点#

using System;
using System.Collections.Generic;

/*
public class ListNode
{
    public int val;
    public ListNode next;

    public ListNode (int x)
    {
        val = x;
    }
}
*/

class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @param n int整型
     * @return ListNode类
     */
    public static int Len(ListNode head) {
        if (head == null) return 0;
        int len = 1;
        ListNode t = head;
        while (t.next != null) {
            t = t.next;
            ++len;
        }
        return len;
    }
    public ListNode removeNthFromEnd(ListNode head, int n) {
        // write code here
        int len = Len(head);
        if (len < n) return null;
        ListNode pre = head;
        ListNode cur = head;
        for (int i = 1; i <= len - n; i++) {
            pre = cur;
            cur = cur.next;
        }
        if (cur == head) { //如果找到的倒数n个结点刚刚好是头结点
            head = pre.next;
        } else {
            pre.next = cur.next;
        }
        return head;
    }
}