這題題目大致意思就是找它所有的.能否滿足五字格，簡單遍歷就好，直接上代碼

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn = 100;
char a[maxn][maxn];
int lazy[maxn][maxn];
int main()
{
    int x;
    cin >> x;
    
    memset(lazy, 
 
0, sizeof(lazy));
    int ans = 0;
    for (int i = 0; i < x; i++)
    {
        getchar();
        for (int  j = 0; j < x; j++)
        {
            scanf("%c", &a[i][j]);
            if (a[i][j] == ‘.‘)
            {
                ans++;
                lazy[i][j] = 1;
            }
        }
    }
    
 
int sum = 0;
    for (int i = 0; i < x; i++)
    {
        for (int j = 0; j < x; j++)
        {
            if (lazy[i][j] == 0||lazy[i][j]==2)continue;
            if (lazy[i][j] == 1)
            {
                if (lazy[i - 1][j] == 1 && lazy[i + 1][j] == 1 && lazy[i][j - 1
 
] == 1 && lazy[i][j + 1] == 1)
                {
                    sum += 5;
                    lazy[i][j] = 2;
                    lazy[i - 1][j] = 2;
                    lazy[i + 1][j] = 2;
                    lazy[i][j + 1] = 2;
                    lazy[i][j - 1] = 2;
                }
            }
        }
    }
    if (sum == ans)
    {
        printf("YES\n");
    }
    else
    {
        printf("NO\n");
    }
}

Codeforces Round #556 (Div. 2) B. Tiling Challenge