解题报告 『[HNOI2003]激光炸弹（前缀和）』

原题地址

前缀和水题，没什么好讲的，注意横纵坐标加1。

另外此题空间有点紧。

 

代码实现如下：

#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (register int i = (a); i <= (b); i++)

const int maxn = 5e3 + 5;

int n, m, N, R;
int a[maxn][maxn];

int MAX(int a, int b) {return a > b ? a : b;}

int read() {
    int x = 0, flag = 0;
    char ch = ' ';
    while (ch != '-' && (ch < '0' || ch > '9')) ch = getchar();
    if (ch == '-') {
        flag = 1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = (x << 1) + (x << 3) + (ch ^ '0');
        ch = getchar();
    }
    return flag ? -x : x;
}

void write(int x) {
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    if (x > 9) write(x / 10);
    putchar(x % 10 + '0');
}

int main() {
    N = read(), R = read();
    n = R, m = R;
    rep(i, 1, N) {
        int x, y, w;
        x = read(), y = read(), w = read();
        x++, y++;
        a[x][y] = w;
        n = MAX(n, x);
        m = MAX(m, y);
    }
    rep(i, 1, n)
        rep(j, 1, m)
            a[i][j] += a[i - 1][j] + a[i][j - 1] - a[i - 1][j - 1];
    int ans = 0;
    rep(i, R, n)
        rep(j, R, m)
            ans = MAX(ans, a[i][j] - a[i - R][j] - a[i][j - R] + a[i - R][j - R]);
    write(ans);
    return 0;
}