C# Console permütasyon ve kombinasyon

C# Console permütasyon ve kombinasyon
{
private static bool NextCombination(IList<int> num, int n, int k)
  {
    bool finished;
    var changed = finished = false;
    if (k <= 0) return false;
    for (var i = k - 1; !finished && !changed; i--)
    {
      if (num[i] < n - 1 - (k - 1) + i)
      {
        num[i]++;
        if (i < k - 1)
          for (var j = i + 1; j < k; j++)
            num[j] = num[j - 1] + 1;
        changed = true;
      }
      finished = i == 0;
    }
    return changed;
  }
 
       
        static IEnumerable<IEnumerable<T>>
        GetCombinations<T>(IEnumerable<T> list, int length) where T : IComparable
        {
            if (length == 1) return list.Select(t => new T[] { t });
            return GetCombinations(list, length - 1)
                .SelectMany(t => list.Where(o => o.CompareTo(t.Last()) > 0),
                    (t1, t2) => t1.Concat(new T[] { t2 }));
        }
 
        static IEnumerable<IEnumerable<T>>
        GetPermutations<T>(IEnumerable<T> list, int length)
        {
            if (length == 1) return list.Select(t => new T[] { t });
            return GetPermutations(list, length - 1)
                .SelectMany(t => list.Where(o => !t.Contains(o)),
                    (t1, t2) => t1.Concat(new T[] { t2 }));
        }
 
        private static void Main()
        {
            int countP = 0, countC = 0;
            const int k = 2;
            var n = new[] { "1", "2","3"};
 
            Console.Write("n: ");
            foreach (var item in n)
            {
                Console.Write("{0} ", item);
            }
            Console.WriteLine();
            Console.WriteLine("k: {0}", k);
            Console.WriteLine();
            Console.WriteLine("===============================");
            Console.WriteLine("Permutations");
            Console.WriteLine("===============================");
            foreach (IEnumerable<string> i in GetPermutations(n, k))
            {
                Console.WriteLine(string.Join(" ", i));
                countC++;
            }
            Console.WriteLine("Count : "+countC);
 
            Console.WriteLine();
            Console.WriteLine("===============================");
            Console.WriteLine("Combinations");
            Console.WriteLine("===============================");
            foreach (IEnumerable<string> i in GetCombinations(n, k))
            {
                Console.WriteLine(string.Join(" ", i));
                countP++;
            }
            Console.WriteLine("Count : " + countP);
 
            Console.ReadKey();
        }
 
}