bzoj 1218: [HNOI2003]激光炸弹

思路：二维前缀和， 枚举矩形左上端点。

 #include<bits/stdc++.h>
 #define LL long long
 #define fi first
 #define se second
 #define mk make_pair
 #define pii pair<int,int>
 #define piii pair<int, pair<int,int>>

 using namespace std;

 const int N =  + ;
 const int M = 1e4 + ;
 const int inf = 0x3f3f3f3f;
 const LL INF = 0x3f3f3f3f3f3f3f3f;
 const int mod = 1e9 + ;

 int n, r, a[N][N];

 int cal(int x, int y) {
     return a[x][y];
 }
 int main() {
     scanf("%d%d", &n, &r);
     for(int i = ; i <= n; i++) {
         int x, y, v; scanf("%d%d%d", &x, &y, &v);
         x++; y++;
         a[x][y] += v;
     }

     for(int i = ; i <= ; i++) {
         for(int j = ; j <= ; j++) {
                 a[i][j] += a[i - ][j] + a[i][j - ] - a[i - ][j - ];
         }
     }

     int ans = ;
     for(int i = ; i <= ; i++) {
         for(int j = ; j <= ; j++) {
             int x = i + r - ;
             int y = j + r - ;
             x = min(x, );
             y = min(y, );
             int ret = cal(x, y) - cal(i - , y) - cal(x, j - ) + cal(i - , j - );
             ans = max(ans, ret);
         }
     }
     printf("%d\n", ans);
     return ;
 }

 /*
 */