bool isPalindrome(struct ListNode* head){
    int vals[500001], vals_num = 0;
    while (head != NULL) {
        vals[vals_num++] = head->val;
        head = head->next;
    }
    for (int i = 0, j = vals_num - 1; i < j; ++i, --j) {
        if (vals[i] != vals[j]) {
            return false;
        }
    }
    return true;
}