Forest density

#include <iostream>
#include <vector>
#include <numeric>
#include <cstdint>

int main() {
    int n, q;
    std::cin >> n >> q;

    std::vector<std::vector<int>> tree_sum(n, std::vector<int>(n));
    for (auto &row : tree_sum) {
        for (auto &tree : row) {
            char c;
            std::cin >> c;
            if (c == '.') tree = 0;
            else tree = 1;
        }
    }

    for (int i = 0; i < n; ++i) {
        for (int j = 1; j < n; ++j) {
            tree_sum[i][j] += tree_sum[i][j-1];
        }
    }
    for (int j = 0; j < n; ++j) {
        for (int i = 1; i < n; ++i) {
            tree_sum[i][j] += tree_sum[i-1][j];
        }
    }

    std::vector<int> outputs(q);

    for (int i = 0; i < q; ++i) {
        int y_1, x_1, y_2, x_2;
        std::cin >> y_1 >> x_1 >> y_2 >> x_2;

        int A = tree_sum[y_2-1][x_2-1];
        int B = 0, C = 0, D = 0;
        if (x_1-1 >= 1) B = tree_sum[y_2-1][x_1-2];
        if (y_1-1 >= 1) C = tree_sum[y_1-2][x_2-1];
        if (x_1-1 >= 1 && y_1-1 >= 1) D = tree_sum[y_1-2][x_1-2];

        outputs[i] = A + D - B - C;
    }
    for (int i = 0; i < q; ++i) {
        std::cout << outputs[i] << std::endl;
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED