class Solution {
public:
void recursion(ListNode* head, vector<int>& res){
if(head != NULL){
__(1)__
res.push_back(head->val);
}
}
vector<int> printListFromTailToHead(ListNode* head) {
vector<int> res;
recursion(head, res);
return res;
}
};
（1）处应为 recursion(head->next,res);
函数的时间复杂度为O(n)