bzoj 1218: [HNOI2003]激光炸弹

Posted 2020-11-07 notnight

思路：二维前缀和， 枚举矩形左上端点。

 

 1 #include<bits/stdc++.h>
 2 #define LL long long
 3 #define fi first
 4 #define se second
 5 #define mk make_pair
 6 #define pii pair<int,int>
 7 #define piii pair<int, pair<int,int>>
 8 
 9 using namespace std;
10 
11 const int N = 5000 + 7;
12 const int M = 1e4 + 7;
13 const int inf = 0x3f3f3f3f;
14 const LL INF = 0x3f3f3f3f3f3f3f3f;
15 const int mod = 1e9 + 7;
16 
17 int n, r, a[N][N];
18 
19 int cal(int x, int y) {
20     return a[x][y];
21 }
22 int main() {
23     scanf("%d%d", &n, &r);
24     for(int i = 1; i <= n; i++) {
25         int x, y, v; scanf("%d%d%d", &x, &y, &v);
26         x++; y++;
27         a[x][y] += v;
28     }
29 
30     for(int i = 1; i <= 5001; i++) {
31         for(int j = 1; j <= 5001; j++) {
32                 a[i][j] += a[i - 1][j] + a[i][j - 1] - a[i - 1][j - 1];
33         }
34     }
35 
36     int ans = 0;
37     for(int i = 1; i <= 5001; i++) {
38         for(int j = 1; j <= 5001; j++) {
39             int x = i + r - 1;
40             int y = j + r - 1;
41             x = min(x, 5001);
42             y = min(y, 5001);
43             int ret = cal(x, y) - cal(i - 1, y) - cal(x, j - 1) + cal(i - 1, j - 1);
44             ans = max(ans, ret);
45         }
46     }
47     printf("%d\n", ans);
48     return 0;
49 }
50 
51 /*
52 */