Combinatorics

class Program
    {
        static int[] elements;
        static bool[] used;
        static int[] permutate;

        static void Gen (int index)
        {
            if (index >= elements.Length)
            {
                Console.WriteLine(string.Join(',', permutate));
            }
            else
            {
                for (int i = 0; i < elements.Length; i++)
                {
                    if (!used[i])
                    {
                        used[i] = true;
                        permutate[index] = elements[i];
                        Gen(index + 1);
                        used[i] = false;
                    }
                }
            }
        }

        static int[] variations;
        static void GenVar(int index, int k)
        {
            if (index >= k)
            {
                Console.WriteLine(string.Join(',', variations));
            }
            else
            {
                for (int i = 0; i < elements.Length; i++)
                {
                    if (!used[i])
                    {
                        used[i] = true;
                        variations[index] = elements[i];
                        GenVar(index + 1, k);
                        used[i] = false;
                    }
                }
            }
        }

        static void PrintPascalTriangle(int height)
        {
            long[][] triangle = new long[height + 1][];
            for (int row = 0; row < height; row++)
            {
                triangle[row] = new long[row + 1];
            }
            triangle[0][0] = 1;
            for (int row = 0; row < height - 1; row ++)
            {
                for (int col = 0; col <= row; col++)
                {
                    triangle[row + 1][col] += triangle[row][col];
                    triangle[row + 1][col + 1] += triangle[row][col];
                }
            }

            for (int row = 0; row < height; row++)
            {
                Console.Write("".PadLeft((height - row) * 2));
                for (int col = 0; col <= row; col++)
                {
                    Console.Write("{0,3} ", triangle[row][col]);
                }
                Console.WriteLine();
            }
        }

        static void Main(string[] args)
        {
            elements = new int[]{ 1, 2, 3, 4, 5 };
            used = new bool[5];
            permutate = new int[5];
            variations = new int[2];
            GenVar(0, 2);
            PrintPascalTriangle(12);
        }
    }