4. 从尾到头打印链表

1  题目描述

       输入一个链表的头节点，从尾到头反过来返回每个节点的值（用数组返回）。

2  思路

       栈、递归、reverse

3  代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> res;
    vector<int> reversePrint(ListNode* head) {
        //reverse
        /*
        while(head) {
            res.push_back(head->val);
            head = head->next;
        }
        //使用algorithm算法中的reverse反转res
        reverse(res.begin(), res.end());
        return res;
        */

        //栈
        /*
        stack<int> s;
        //入栈
        while(head) {
            s.push(head->val);
            head = head->next;
        }
        //出栈
        while(!s.empty()) {
            res.push_back(s.top());
            s.pop();
        }
        return res;
        */

        //递归

        if(head == nullptr) {
            return res;
        }
        reversePrint(head->next);
        res.push_back(head->val);
        return res;
    }
};