bool isPopOrder(vector<int> pushV,vector<int> popV) {
    if (pushV.size() != popV.size()) {
        return false;
    }

    int n = pushV.size();

    stack<int> myStack;
    int i = 0, j = 0;
    while (i < n) {
        int cur = popV[i];
        // check stack
        if (!myStack.empty() && myStack.top() == cur) {
            myStack.pop();
            i++;
            continue;
        }
        // check vector
        while (j < n && pushV[j] != cur) {
            myStack.push(pushV[j]);
            j++;
        }
        if (j == n) {
            return false;
        }

        i++;
        j++;
    }

    return i == n;
}