3.从尾到头打印链表

输入一个链表，按链表值从尾到头的顺序返回一个ArrayList

解决方案：利用栈来完成

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

//利用栈stack
public class TailToHead {
    public static void main(String[] args) {
        ListNode node1 =new ListNode(10);
        ListNode node2 =new ListNode(20);
        ListNode node3 =new ListNode(30);
        ListNode node4 =new ListNode(40);
        node1.next=node2;
        node2.next=node3;
        node3.next=node4;
        ArrayList<Integer> list = printListFromTailToHead(node1);
        for (Integer integer : list) {
            System.out.println(integer);
        }
        
    }

    static class ListNode {
        int val;
        ListNode next = null;

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

    public static ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
        ArrayList<Integer> aList = new ArrayList<Integer>();
        Stack<Integer> stack = new Stack<Integer>();
        // 若链表为空
        if (listNode == null) {
            return aList;
        }
        while (listNode != null) {
            stack.push(listNode.val);
            listNode = listNode.next;
        }
        while (!stack.isEmpty()) {
            aList.add(stack.pop());
        }
        return aList;
    }

}