题目描述

输入一个链表，按链表值从尾到头的顺序返回一个ArrayList

题目链接：https://www.nowcoder.com/practice/d0267f7f55b3412ba93bd35cfa8e8035

解题思路

借助栈

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

使用递归的方式

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

借助链表原地反转的思想

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