/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(head == NULL) return head;
        ListNode* cur = head;
        stack<ListNode*> node;
        while(cur != NULL){
            node.push(new ListNode(cur->val));
            cur = cur->next;
        }
        head = node.top();
        node.pop();
        cur = head; 
        while(!node.empty()){
            cur->next = node.top();
            cur = cur->next;
            node.pop();
        }
        return head; 
    }
};