void solve(int m,int n)
{
     if(check(m,n))
     {
                   ans++;
                   visited[m][n]=true;
                   solve(m-1,n);
                   solve(m+1,n);
                   solve(m,n-1);
                   solve(m,n+1);
       }
}
递归四次没剪枝这是O(4^n)⊙﹏⊙b汗