题解：P14209 [ROI 2016 Day2] 视频监控管理

#include <bits/stdc++.h>
using namespace std;
const int N=2e3+10;
int n,m,a[N][N],b[N][N],sum[N][N];
int main()
{
	freopen("room.in","r",stdin);
	freopen("room.out","w",stdout);
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=m;j++)
		{
			char c;cin>>c;
			a[i][j]=a[i+n][j]=a[i][j+m]=a[i+n][j+m]=c-'0';
		}
	}
	for(int i=2;i<=2*n;i++)
	{
		for(int j=2;j<=2*m;j++)
		{
			if(a[i][j]==a[i-1][j]&&a[i][j]==a[i][j-1]&&a[i][j]==a[i-1][j-1]) b[i][j]=1;
			else b[i][j] = 0; 
		}
	}
	for(int i=1;i<=2*n;i++)
	{
		for(int j=1;j<=2*m;j++)
		{
			sum[i][j]=sum[i-1][j]+sum[i][j-1]-sum[i-1][j-1]+b[i][j];
		}
	}
	int ans=0;
	for(int i=n+1;i<=2*n;i++)
	{
		for(int j=m+1;j<=2*m;j++)
		{
			int now=sum[i][j]-sum[i-n+1][j]-sum[i][j-m+1]+sum[i-n+1][j-m+1];
			ans=max(ans,now);
		}
	}
	cout<<ans;
	return 0;
}