Forest density

#include <iostream>
#include <vector>
 
using namespace std;
 
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int n, q;
    cin >> n >> q;
 
    // Create the forest grid and prefix sum array
    vector<vector<int>> prefix(n + 1, vector<int>(n + 1, 0));
 
    // Read the forest map and build the prefix sum array
    for (int i = 1; i <= n; i++) {
        string row;
        cin >> row;
        for (int j = 1; j <= n; j++) {
            // Prefix sum formula
            prefix[i][j] = (row[j - 1] == '*' ? 1 : 0) + 
                           prefix[i - 1][j] + 
                           prefix[i][j - 1] - 
                           prefix[i - 1][j - 1];
        }
    }
 
    // Answer each query
    for (int i = 0; i < q; i++) {
        int y1, x1, y2, x2;
        cin >> y1 >> x1 >> y2 >> x2;
 
        // Calculate the number of trees in the rectangle using the prefix sum
        int result = prefix[y2][x2] - 
                     prefix[y1 - 1][x2] - 
                     prefix[y2][x1 - 1] + 
                     prefix[y1 - 1][x1 - 1];
 
        cout << result << '\n';
    }
 
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED