【HNOI 2003】 激光炸弹

【题目链接】

https://www.lydsy.com/JudgeOnline/problem.php?id=1218

【算法】

二维前缀和

【代码】

#include<bits/stdc++.h>
using namespace std;
#define calc(xa,ya,xb,yb) s[xb][yb] - s[xa-1][yb] - s[xb][ya-1] + s[xa-1][ya-1]

int n,r,i,j,x,y,c,mx;
int s[][];

template <typename T> inline void read(T &x)
{
    int f = ; x = ;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
    for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';
    x *= f;
}
template <typename T> inline void write(T x)
{
    if (x < )
    {
        putchar('-');
        x = -x;
    }
    if (x > ) write(x/);
    putchar(x%+'');
}
template <typename T> inline void writeln(T x)
{
    write(x);
    puts("");
}

int main() {

        read(n); read(r);
        for (i = ; i <= n; i++)
        {
                read(x); read(y); read(c);
                s[x+][y+] += c;
        }
        for (i = ; i <= ; i++)
        {
                for (j = ; j <= ; j++)
                {
                        s[i][j] = s[i-][j] + s[i][j-] - s[i-][j-] + s[i][j];
                }
        }
        for (i = r; i <= ; i++)
        {
                for (j = r; j <= ; j++)
                {
                        if (calc(i-r+,j-r+,i,j) > mx)
                                mx = calc(i-r+,j-r+,i,j);
                }
        }
        writeln(mx);

        return ;

}