Forest density

#include <iostream>
#include <vector>
#include <string>

using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int n, q;
    cin >> n >> q;

    vector<vector<int>> pref(n + 1, vector<int>(n + 1, 0));

    for (int y = 1; y <= n; ++y) {
        string row;
        cin >> row;
        for (int x = 1; x <= n; ++x) {
            int has_tree = (row[x - 1] == '*') ? 1 : 0;
            pref[y][x] = has_tree 
                       + pref[y - 1][x] 
                       + pref[y][x - 1] 
                       - pref[y - 1][x - 1];
        }
    }

    while (q--) {
        int y1, x1, y2, x2;
        cin >> y1 >> x1 >> y2 >> x2;

        int result = pref[y2][x2] 
                   - pref[y1 - 1][x2] 
                   - pref[y2][x1 - 1] 
                   + pref[y1 - 1][x1 - 1];

        cout << result << endl;
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED