luoguP2280 [HNOI2003] laser bombs

luoguP2280 [HNOI2003] laser bombs

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And two-dimensional prefix

#include<bits/stdc++.h>

using namespace std;

const int MAXN = 5000 + 10;

inline int read()
{
    int f=1,x=0;
    char ch;
    do
    {
        ch=getchar();
        if(ch=='-') f=-1;
    }while(ch<'0'||ch>'9');
    do
    {
        x=(x<<3)+(x<<1)+ch-'0';
        ch=getchar();
    }while(ch>='0'&&ch<='9');
    return f*x;
} 

int t,r;
int sum[MAXN][MAXN];

int main()
{
    t=read();r=read();
    for(int i=1;i<=t;i++)
    {
        int x=read(),y=read(),v=read();
        sum[x+1][y+1]=v; 
    }
    for(int i=1;i<=5000 + 1;i++)
        for(int j=1;j<=5000 + 1;j++)
            sum[i][j]=sum[i-1][j]+sum[i][j-1]+sum[i][j]-sum[i-1][j-1];
    int ans=0;
    for(int i=0;i<=5000 + 1-r;i++)
        for(int j=0;j<=5000 + 1-r;j++)
            ans=max(ans,sum[i+r][j+r]-sum[i+r][j]-sum[i][j+r]+sum[i][j]);
    cout<<ans<<endl;
            
}