Arrays.21.Combinations.cs

using System;

class Combinations
{
    static void Main()
    {
        Console.WriteLine("Enter the number of elements:");
        long numberOfElements = long.Parse(Console.ReadLine());
        Console.WriteLine("Enter K:");
        long K = long.Parse(Console.ReadLine());
        long[] elements = new long[numberOfElements];
        string subset = "";
        int lenCounter = 0;
        for (int i = 0; i < elements.Length; i++)
        {
            Console.WriteLine("Enter element № {0}", i + 1);
            elements[i] = long.Parse(Console.ReadLine());
        }
        int maxSubsets = (int)Math.Pow(2, numberOfElements);
        for (int i = 1; i < maxSubsets; i++)
        {
            subset = "";
            for (int j = 0; j <= numberOfElements; j++)
            {
                int mask = 1 << j;
                int nAndMask = i & mask;
                int bit = nAndMask >> j;
                if (bit == 1)
                {
                    subset = subset + " " + elements[j];
                    lenCounter++;
                }
            }
            if (lenCounter == K)
            {
                Console.WriteLine(subset);
            }
            lenCounter = 0;
        }
    }
}