二维数组前缀和！！！

acwing 99 激光炸弹

题解有人写扫描线，Orz Orz Orz

前缀和嘛，固定区间，具体上图

公式都摆出来了，上代码

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#define maxn 5010
using namespace std;
int map[maxn][maxn];
int n, m;
int main() {
	scanf("%d %d", &n, &m);
	int nn = m, mm=m;
	int x, y, val;
	while (n--) {
		scanf("%d%d%d", &x, &y, &val);
		x++;
		y++;
		map[x][y] = val;
		nn = max(nn, x);
		mm = max(mm, y);
	}
	for (int i = 1; i <= nn; i++) {
		for (int j = 1; j <= mm; j++) {
			map[i][j] = map[i - 1][j] + map[i][j - 1] - map[i - 1][j - 1] + map[i][j];
		}
	}
	int ans = 0;
	for (int i = m; i <= nn; i++) {
		for (int j = m; j <= mm; j++) {
			ans = max(ans, map[i][j] + map[i - m][j - m] - map[i - m][j] - map[i][j - m]);
		}
	}
	printf("%d
", ans);

	return 0;
}