题解 | #输出单向链表中倒数第k个结点#

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()) {
            int num = sc.nextInt();
            //构建带有头节点的链表
            ListNode head = new ListNode();
            ListNode tmp = head;//head不移动，利用辅助变量来遍历
            for (int i = 0; i < num; i++) {
                ListNode node = new ListNode(sc.nextInt());
                tmp.next = node;
                tmp = tmp.next;//tmp后移
            }
            int k = sc.nextInt();
            if (getKthNodeFromEnd(head, k) != null) {
                System.out.println(getKthNodeFromEnd(head, k).val);
            } else System.out.println(0);

        }
    }

    public static ListNode getKthNodeFromEnd(ListNode head, int k) {//获取链表倒数第k个节点的方法
        int len = getLength(head);//题目要求构建后要忘记链表长度，自己重新获取链表长度
        if (len == 0 || k > len) {//空链表或者k超过链表长度，返回null
            return null;
        }
        ListNode tmp = head;
        for (int i = 0; i < len - k + 1; i++) {//从head-0开始，正数第n-k+1个，就是倒数第k个
            tmp = tmp.next;
        }
        return tmp;
    }

    public static int getLength(ListNode head) {//传入链表头节点，获取该链表长度
//        if (head.next == null) {//空链表
//            return 0;
//        }
        int length = 0;
        ListNode tmp = head.next;//定义辅助变量用于遍历
        while (tmp != null) {
            length++;
            tmp = tmp.next;//指针后移
        }
        return length;
    }
}

class ListNode {//定义节点
    int val;
    ListNode next;
    ListNode(){//默认空构造器

    };
    ListNode(int val) {//构造器
        this.val = val;
        next = null;
    }
}