99. 激光炸弹

Posted 2021-03-11 doubest

题目链接：

https://www.acwing.com/problem/content/101/

 

题解：

边界问题最复杂，画图好好模拟一下，二维前缀和还是比较容易的

枚举的所有的边长为R的正方形，AC代码是枚举的正方形的左上端点。

 

AC代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>

using namespace std;

int const N = 5010;

int s[N][N];
int xm,ym;
int r;


int main(void){
    int n,r;
    int x,y,w;
    scanf("%d%d",&n,&r);
    
    r = min(5001,r);
    xm = ym = 5000;
    while(n--){
        scanf("%d%d%d",&x,&y,&w);
        x++;y++;
        s[x][y] = w;
    }

    
    for(int i=1;i<=xm;i++){
        for(int j=1;j<=ym;j++){
            s[i][j] = s[i-1][j] + s[i][j-1] - s[i-1][j-1] + s[i][j];
        }
    }
    
    
    int res = 0;
    for(int i=1;i+r-1<=xm;i++){
        for(int j=1;j+r-1<=ym;j++){
            int x1 = i,y1 = j;
            int x2 = i+r-1,y2= j+r-1;
            int sum = s[x2][y2] - s[x1-1][y2] - s[x2][y1-1] + s[x1-1][y1-1];
            res = max(sum,res);
        }
    }
    
    printf("%d
",res);
    return 0;
}