激光炸弹（二维前缀和）

  1 #include <iostream>
  2 #include <algorithm>
  3 #include <cstring>
  4 using namespace std;
  5 
  6 const int N = 5e3 + 5;
  7 int g[N][N];
  8 int main(){
  9     int N,R;
 10     cin >> N >> R;
 11     int n = R, m = R;
 12     for(int i = 0, x, y, w; i < N; ++ i)
 13     {
 14         cin >> x >> y >> w;
 15         x++,y++;
 16         n = max(x,n), m = max(m, y);
 17         g[x][y] += w;
 18     }
 19     for(int i = 1; i <= n; ++ i)//求前缀和 
 20         for(int j = 1; j <= m; ++ j)
 21             g[i][j] += g[i-1][j] + g[i][j-1] - g[i-1][j-1];
 22     int ans = 0;
 23     for(int i = R; i <= n; ++ i)
 24         for(int j = R; j <= m; ++ j)
 25             ans = max(ans, g[i][j] - g[i-R][j] - g[i][j-R] + g[i-R][j-R]);//枚举正方形 
 26     cout << ans << endl;
 27     return 0;
 28 }