Codeforces round 1059(B. Forgery)

///Bismillahir Rahmanir Rahim

///Author: Tanvir Ahmmad

///CSE,Islamic University,Bangladesh

#include<iostream>

#include<cstdio>

#include<algorithm>

#include<string>

#include<cstring>

#include<sstream>

#include<cmath>

#include<cstring>

#include<vector>

#include<queue>

#include<map>

#include<set>

#include<stack>

#include<vector>

#include<iterator>

#include <functional> ///sort(arr,arr+n,greater<int>()) for decrement of array

/*every external angle sum=360 degree

  angle find using polygon hand(n) ((n-2)*180)/n*/

///Floor[Log(b)  N] + 1 = the number of digits when any number is represented in base b

using namespace std;

typedef long long ll;

int main()

{

    ll n,m,flag=1;

    cin>>n>>m;

    string str[n+9],new_str[n+9];

    char rplc='#';

    for(ll i=0; i<n; i++)

        for(ll j=0; j<m; j++)

            new_str[i].append(".");

    for(ll i=0; i<n; i++)

        cin>>str[i];

    for(ll i=1; i<n-1; i++)

        for(ll j=1; j<m-1; j++)

            if(str[i-1][j-1]=='#' && str[i-1][j]=='#' && str[i-1][j+1]=='#' && str[i][j-1]=='#'  && str[i][j+1]=='#' && str[i+1][j-1]=='#' && str[i+1][j]=='#' && str[i+1][j+1]=='#')

            {

                new_str[i-1][j-1] = rplc;

                new_str[i-1][j] = rplc;

                new_str[i-1][j+1] = rplc;

                new_str[i][j-1] = rplc;

                new_str[i][j+1] = rplc;

                new_str[i+1][j-1] = rplc;

                new_str[i+1][j] = rplc;

                new_str[i+1][j+1] = rplc;

            }

    for(ll i=0; i<n; i++)

        for(ll j=0; j<m; j++)

            if(str[i][j]!=new_str[i][j])

                flag=0;

    if(flag==1)

        cout<<"YES"<<endl;

    else

        cout<<"NO"<<endl;

    return 0;

}

///Alhamdulillah

Problem link:https://codeforces.com/problemset/problem/1059/B