[Luogu] 无线网络发射器选址

https://www.luogu.org/problemnew/show/P2038

二维前缀和

#include <iostream>
#include <cstdio>

using namespace std;
const int N = ;
const int n = ;

int A[N][N];
int d, T;

#define gc getchar()

inline int read() {
    int x = ; char c = gc;
    while(c < '' || c > '') c = gc;
    while(c >= '' && c <= '') x = x *  + c - '', c = gc;
    return x;
}

int main() {
    d = read(); T = read();
    for(int i = ; i <= T; i ++) {
        int x = read(), y = read(), w = read();
        A[x + ][y + ] = w;
    }
    for(int i = ; i <= n; i ++)
        for(int j = ; j <= n; j ++)
            A[i][j] += (A[i - ][j] + A[i][j - ] - A[i - ][j - ]);
    int js(), Max();
    for(int i = ; i <= n; i ++) {
        for(int j = ; j <= n; j ++) {
            int x_1 = max(, i - d - ), y_1 = max(, j - d - ), x_2 = min(n, i + d), y_2 = min(n, j + d);
            int W = A[x_2][y_2] - A[x_2][y_1] - A[x_1][y_2] + A[x_1][y_1];
            if(W > Max) {
                Max = W; js = ;
            } else if(W == Max) js ++;
        }
    }
    cout << js << " " << Max;
    return ;
}