/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* p = head;
        vector<int> stack;
        int size_=0;
        while(p)
        {
            stack.push_back(p->val);
            size_++;
            p=p->next;
        }
        int i = 0;
        ListNode* q = head;
        while(i<size_)
        {
            cout<<stack.back()<<" ";
            q->val = stack.back();
            stack.pop_back();
            q = q->next;
            i++;

        }
        return head;

    }
};