/**
 * 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:
    bool isPalindrome(ListNode* head) {
        stack<int> mystack;
        int node_num = 0;
        ListNode *tmp = head;
        while(tmp != nullptr)
        {
            tmp = tmp->next;
            node_num ++;
        }
        tmp = head;
        for(int i=1 ; i<=node_num ;i++)
        {
            if(i<=node_num/2) mystack.push(tmp->val);
            if(i>node_num/2+node_num%2)
            {
                if(tmp->val != mystack.top()) return false;
                mystack.pop();
            } 
            tmp = tmp->next;
        }
        return true;
    }
};