【剑指offer】面试题 6. 从尾到头打印链表

面试题 6. 从尾到头打印链表

NowCoder

题目描述

输入一个链表的头结点，从尾到头反过来打印出每个结点的值。

Java 实现

ListNode Class

class ListNode {
	int val;
	ListNode next = null;

	ListNode(int val) {
		this.val = val;
	}

	@Override
	public String toString() {
		return val + "->" + next;
	}
}

使用递归

import java.util.ArrayList;

public class Solution {
	public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
		ArrayList<Integer> res = new ArrayList<>();
		if (listNode == null) {
			return res;
		}
		res.addAll(printListFromTailToHead(listNode.next));
		res.add(listNode.val);
		return res;
	}
}

使用头插法

import java.util.ArrayList;

public class Solution {
	public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
		ArrayList<Integer> res = new ArrayList<>();
		ListNode head = new ListNode(-1);
		while (listNode != null) {
			ListNode newHead = listNode.next;
			listNode.next = head.next;
			head.next = listNode;
			listNode = newHead;
		}
		while (head.next != null) {
			res.add(head.next.val);
			head = head.next;
		}
		return res;
	}
}

使用栈

import java.util.ArrayList;
import java.util.Stack;

public class Solution {
	public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
		ArrayList<Integer> res = new ArrayList<>();
		Stack<Integer> stack = new Stack<>();
		while (listNode != null) {
			stack.push(listNode.val);
			listNode = listNode.next;
		}
		while (!stack.isEmpty()) {
			res.add(stack.pop());
		}
		return res;
	}
}