codeforces_B. Forgery

http://codeforces.com/contest/1059/problem/B

题意：

For simplicity, the signature is represented as an $\mathrm{n\times mn\times m grid,\; where\; every\; cell\; is\; either\; filled\; with\; ink\; or\; empty.\; Andrey\text{'}s\; pen\; can\; fill\; a 3\times 33\times 3square\; without\; its\; central\; cell\; if\; it\; is\; completely\; contained\; inside\; the\; grid,\; as\; shown\; below.}$

xxx
x.x
xxx

Determine whether is it possible to forge the signature on an empty $\mathrm{n\times mn\times m grid.}$

$\mathrm{思路：}$

$\mathrm{模拟。在给定的签名中寻找特定的点，该点的所有相邻点均被涂色，找到该点，将另一张空白纸上的该点相邻的点涂色，最后比较两张图是否相同。}$

#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
#define LL long long

char a[1005][1005],b[1005][1005];

bool legal(int x,int y)
{
    for(int i=-1; i<=1; i++)
        for(int j=-1; j<=1; j++)
        {
            if(i==0&&j==0)
                continue;
            if(a[x+i][y+j]=='.')
                return 0;
        }
    return 1;
}

void draw(int x,int y)
{
    for(int i=-1; i<=1; i++)
        for(int j=-1; j<=1; j++)
        {
            if(i==0&&j==0)
                continue;
            b[x+i][y+j]='#';
        }
}

int n,m;
bool compareAB()
{
    for(int i=0; i<n; i++)
        for(int j=0; j<m; j++)
            if(a[i][j]!=b[i][j])
                return 0;
    return 1;
}

int main()
{

    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(int i=0;i<n;i++)
            for(int j=0;j<m;j++)
                b[i][j]='.';
        for(int i=0; i<n; i++)
            scanf("%s",a[i]);
        for(int i=1; i<n-1; i++)
            for(int j=1; j<m-1; j++)
            {
                if(legal(i,j))
                    draw(i,j);
            }
        if(compareAB())
            printf("YES
");
        else
            printf("NO
");
    }
    return 0;
}