题解 | #删除链表的倒数第n个节点#注意删除头节点的情况

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @param n int整型 
     * @return ListNode类
     */
    public ListNode removeNthFromEnd (ListNode head, int n) {
        // write code here
        //第一步计算长度
        if(head == null || head.next == null){
            return null;
        }
        int length = 0;
        ListNode temp = head;
        while(temp != null){
            length ++;
            temp = temp.next;
        }
        if(length == n){
            return head.next;
        }
        //第二步 找到倒数第n个节点的前一个节点
        int target = length - n -1;
        temp = head;
        for(int i = 0;i<target; i++){
            temp = temp.next;
        }
        temp.next = temp.next.next;
        return head;
    }
}