从尾到头打印链表

题目描述

输入一个链表，按链表从尾到头的顺序返回一个ArrayList。

法一：非递归

/**
*  struct ListNode {
*        int val;
*        struct ListNode *next;
*        ListNode(int x) :
*              val(x), next(NULL) {
*        }
*  };
*/
class Solution {
public:
    vector<int> printListFromTailToHead(ListNode* head) {
        vector<int> ans;
        while(head){
            ans.push_back(head -> val);
            head = head -> next;
        }
        reverse(ans.begin(), ans.end());
        return ans;
    }
};

法二：非递归

/**
*  struct ListNode {
*        int val;
*        struct ListNode *next;
*        ListNode(int x) :
*              val(x), next(NULL) {
*        }
*  };
*/
class Solution {
public:
    vector<int> printListFromTailToHead(ListNode* head) {
        vector<int> ans;
        while(head){
            ans.insert(ans.begin(), head -> val);
            head = head -> next;
        }
        return ans;
    }
};

法三：递归

/**
*  struct ListNode {
*        int val;
*        struct ListNode *next;
*        ListNode(int x) :
*              val(x), next(NULL) {
*        }
*  };
*/
class Solution {
public:
    vector<int> printListFromTailToHead(ListNode* head) {
        vector<int> ans;
        if(head != NULL){
            ans = printListFromTailToHead(head -> next);
            ans.push_back(head -> val);
        }
        return ans;
    }
};