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 = 5000 + 7;
const int M = 1e4 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;

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 = 1; i <= n; i++) {
        int x, y, v; scanf("%d%d%d", &x, &y, &v);
        x++; y++;
        a[x][y] += v;
    }

    for(int i = 1; i <= 5001; i++) {
        for(int j = 1; j <= 5001; j++) {
                a[i][j] += a[i - 1][j] + a[i][j - 1] - a[i - 1][j - 1];
        }
    }

    int ans = 0;
    for(int i = 1; i <= 5001; i++) {
        for(int j = 1; j <= 5001; j++) {
            int x = i + r - 1;
            int y = j + r - 1;
            x = min(x, 5001);
            y = min(y, 5001);
            int ret = cal(x, y) - cal(i - 1, y) - cal(x, j - 1) + cal(i - 1, j - 1);
            ans = max(ans, ret);
        }
    }
    printf("%d
", ans);
    return 0;
}

/*
*/