1150B - Tiling Challenge - CodeForces Solution

    #include<bits/stdc++.h>
    #define int long long
    using namespace std;
     
    char a[101][101];
    signed main(){
        ios_base::sync_with_stdio(false);
        cin.tie(0);
        for(int i=0;i<=100;i++){
            for(int j=0;j<=100;j++)
              a[i][j]='#';
        }
        int n;
        cin>>n;
        for(int i=1;i<=n;i++){
            for(int j=1;j<=n;j++){
                cin>>a[i][j];
            }
        }
        bool flag=true;
        for(int i=1;i<=n;i++){
            for(int j=1;j<=n;j++){
                if(a[i][j]=='.'){
                    if(a[i+1][j-1]=='#' || a[i+1][j]=='#' || a[i+1][j+1]=='#' || a[i+2][j]=='#'){
                        flag=false;
                    }
                        a[i][j]=a[i+1][j-1]=a[i+1][j]=a[i+1][j+1]=a[i+2][j]='#';
                }
            }
        }
        	if(flag)
    		cout<<"Yes"<<endl;
    	else
    		cout<<"NO"<<endl;
        return 0;
    }