从尾到头打印链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> printListReversingly(ListNode* head) {
        vector<int> a;
        if(head == NULL){
            return a;
        }else{
            a = printListReversingly(head -> next);
            a.push_back(head -> val);
            return a;
        }
    }
};