MT2056 二阶前缀和

#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 10;
int n, R;
int a[N][N];
int b[N][N];
int main()
{
    cin >> n >> R;
    for (int i = 0; i < n; i++)
    {
        int x, y, v;
        cin >> x >> y >> v;
        x++, y++;
        a[x][y] = a[x][y] + v;
    }
    for (int i = 1; i <= 1005; i++)
    {
        for (int j = 1; j <= 1005; j++)
        {
            b[i][j] = a[i][j] + b[i - 1][j] + b[i][j - 1] - b[i - 1][j - 1];
        }
    }
 
    int ans = 0;
    for (int i = R; i <= 1005; i++)
    {
        for (int j = R; j <= 1005; j++)
        {
            ans = max(ans, b[i][j] - b[i - R][j] - b[i][j - R] + b[i - R][j - R]);
        }
    }
    cout << ans;
    return 0;
}