AcWing 99. 激光炸弹

#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
const int maxn = 5055;
int n, r;
int b[maxn][maxn];
int main()
{
   cin >> n >> r;
   r=min(5001,r);
   int xm = r, ym = r;
   for (int i = 1; i <= n; i++)
   {
      int x, y, w;
      cin >> x >> y >> w;
      x++, y++;
      xm = max(x, xm);
      ym = max(y, ym);
      b[x][y] += w;
   }
   for (int i = 1; i <= xm; i++)
   {
      for (int j = 1; j <= ym; j++)
      {
         b[i][j] += b[i - 1][j] + b[i][j - 1] - b[i - 1][j - 1];
      }
   }
   int res = 0;
   for (int i = r; i <= xm; i++)
   {
      for (int j = r; j <= ym; j++)
      {
         res = max(res, b[i][j] - b[i - r][j] - b[i][j - r] + b[i - r][j - r]);
      }
   }
   cout << res;
}