static bool IsPerfectSubArray(int[,] mat, int size)//Assignment #6
        {
            int sum = 0;
            for (int i = 0; i < size; i++)
                for (int j = 0; j < size; j++)
                {
                    if (i == 0 || i == size - 1 || j == 0 || j == size - 1)
                        sum += mat[i, j];
                    else
                        sum -= mat[i, j];
                }
            return sum == 0;
        }
        static int PerfectSubArrays(int[,] mat)//Assignment #6 Bonus
        {
            int SubArrayMaxSize = Math.Min(mat.GetLength(0), mat.GetLength(1));
            int PerfectSubArraysCounter = 0;
            for (int i = SubArrayMaxSize; i > 2; i--)
                for (int j = 0; j <= mat.GetLength(0) - i; j++)
                    for (int k = 0; k <= mat.GetLength(1) - i; k++)
                    {
                        int[,] mat2 = new int[i, i];
                        for (int p = 0; p < i; p++)
                            for (int q = 0; q < i; q++)
                                mat2[p, q] = mat[p+j, q+k];
                        if (IsPerfectSubArray(mat2, i))
                            PerfectSubArraysCounter++;
                    }
            return PerfectSubArraysCounter;
        }