The Correct Largest Rectangle

#include<iostream>
#include<stack>

using namespace std;

int maxSizeFromHistogram(int a[], int n)
{
    stack<int> s;
    int maxArea = 0;
    int tp;
    int areaWithTop;

    int i = 0;
    while (i < n) {
        if (s.empty() || a[s.top()] <= a[i]) {
            s.push(i++);
        } else {
            tp = s.top(); s.pop();
            int w = s.empty() ? i : i - s.top() - 1;
            areaWithTop = a[tp] * w;

            if (maxArea < areaWithTop)
                maxArea = areaWithTop;
        }
    }

    while (!s.empty()) {
        tp = s.top(); s.pop();
        int w = s.empty() ? i : i - s.top() - 1;
        areaWithTop = a[tp] * w;

        if (maxArea < areaWithTop)
            maxArea = areaWithTop;
    }

    return maxArea;
}

int main()
{
    int n; cin >> n;
    int a[n];
    for (int i = 0; i < n; i++)
        a[i] = 0;
    int _max = 0;
    for (int rowIndex = 0; rowIndex < n; rowIndex++)
    {
        for (int j = 0; j < n; j++)
        {
            int value; cin >> value;
            if (value == 0) a[j]++;
            else a[j] = 0;
        }

        int result = maxSizeFromHistogram(a, n);

        if (_max < result) _max = result;
    }
    cout << "Result: " << _max;
}