Forest density

input/code.cpp: In function 'std::vector<int> prefix_sum(std::vector<int>&)':
input/code.cpp:10:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |     for (int i = 1; i < arr.size(); ++i) {
      |                     ~~^~~~~~~~~~~~
input/code.cpp: In function 'std::vector<std::vector<int> > prefix_sum(std::vector<std::vector<int> >)':
input/code.cpp:20:26: warning: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   20 |     for (size_t j = 1; j < n; j++)
      |                        ~~^~~
input/code.cpp:26:26: warning: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   26 |     for (size_t i = 1; i < n; i++)
      |                        ~~^~~
input/code.cpp:29:30: warning: comparison of integer expressions of different signedne...

#include <bits/stdc++.h>

using namespace std;

#define debug(x) cerr << #x << ': ' << x << endl;

vector<int> prefix_sum(vector<int>& arr) {
    vector<int> psum(arr.size());
    psum[0] = arr[0];
    for (int i = 1; i < arr.size(); ++i) {
        psum[i] = psum[i - 1] + arr[i];
    }
    return psum;
}

vector<vector<int>> prefix_sum(vector<vector<int>> forest) {
    int n = forest.size();
    vector<vector<int>> psum (n, vector<int>(n));
    psum[0][0] = forest[0][0];
    for (size_t j = 1; j < n; j++)
    {
        psum[0][j] = psum[0][j-1] + forest[0][j];
    }


    for (size_t i = 1; i < n; i++)
    {
        psum[i][0] = forest[i][0] + psum[i-1][0];
        for (size_t j = 1; j < n; j++)
        {
            psum[i][j] = forest[i][j] + psum[i-1][j] + psum[i][j-1] - psum[i-1][j-1];
        }
    }

    return psum;
}

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

    vector<vector<int>> forest (n, vector<int>(n));

    for (size_t i = 0; i < n; i++)
    {
        for (size_t j = 0; j < n; j++)
        {
            char c;
            cin >> c;
            forest[i][j] = (c == '.') ? 0 : 1;
        }
    }

    int y1[q], x1[q], y2[q], x2[q];
    for (size_t i = 0; i < q; i++)
    {
        cin >> y1[i] >> x1[i] >> y2[i] >> x2[i];
        y1[i]--;
        x1[i]--;
        y2[i]--;
        x2[i]--;
    }

    vector<vector<int>> psum = prefix_sum(forest);
    

    for (size_t i = 0; i < q; i++)
    {
        int number;
        if (x1[i] > 0 && y1[i] > 0) {
            number = psum[y2[i]][x2[i]] - psum[y2[i]][x1[i]-1] - psum[y1[i]-1][x2[i]] + psum[y1[i]-1][x1[i]-1];
        }
        else if (x1[i] > 0 && y1[i] == 0) {
            number = psum[y2[i]][x2[i]] - psum[y2[i]][x1[i]-1];
        }
        else if (x1[i] == 0 && y1[i] > 0) {
            number = psum[y2[i]][x2[i]] - psum[y1[i]-1][x2[i]];
        }
        else {
            number = psum[y2[i]][x2[i]];
        }

        cout << number << endl;
    }
    

    

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED