combs permutations etc

using System;
using System.Linq;
using System.Collections.Generic;
namespace CombConsole {
    public class Comb {
        public static IEnumerable<List<T>> SubSetsGeneration<T>(T[] input) {
            var resList = new List<List<T>>();
            int n = input.Length;
            int[] a = new int[n + 1];
            while (a[n] != 1) {
                var list = new List<T>();
                for (int i = 0; i < n; i++)
                    if (a[i] == 1)
                        list.Add(input[i]);
                resList.Add(list);
                int j = 0;
                while (a[j] == 1) {
                    a[j] = 0;
                    j++;
                }
                a[j] = 1;
            }
            return resList;
        }
        public static IEnumerable<List<T>> RepetitionPlacing<T>(T[] input, int k) {
            var resList = new List<List<T>>();
            int n = input.Length;
            int[] b = new int[k];
            while (b[k - 1] != n - 1) {
                var list = new List<T>();
                for (int i = 0; i < k; i++)
                    list.Add(input[b[i]]);
                resList.Add(list);
                int j = 0;
                while (b[j] == n - 1) {
                    b[j] = 0;
                    j++;
                }
                b[j]++;
            }
            return resList;
        }
        public static IEnumerable<List<T>> Combinations<T>(T[] input, int k) {
            var resList = new List<List<T>>();
            int n = input.Length;
            int[] b = new int[k];
            for (int i = 0; i < k; i++)
                b[i] = i;
            int ii = 0;
            while (ii != -1) {
                var list = new List<T>();
                for (int i = 0; i < k; i++)
                    list.Add(input[b[i]]);
                resList.Add(list);
                int mx = n - 1;
                ii = k - 1;
                for (; ii >= 0; ii--) {
                    if (b[ii] < mx) {
                        b[ii]++;
                        for (int j = ii + 1; j < k; j++)
                            b[j] = b[j - 1] + 1;
                        break;
                    }
                    mx = b[ii] - 1;
                }
            }
            return resList;
        }
        public static IEnumerable<List<T>> Premutations<T>(T[] input, int k) {
            var resList = new List<List<T>>();
            int n = input.Length;
            int[] b = new int[k];
            for (int i = 0; i < k; i++)
                b[i] = i;
            int ii = 0;
            while (ii != -1) {
                var list = new List<T>();
                for (int i = 0; i < k; i++)
                    list.Add(input[b[i]]);
                resList.Add(list);
                int mx = n - 1;
                for (ii = k-1; ii >= 0; ii--) {
                    if (b[ii] < mx) {
                        b[ii]++;
                        for (int j = ii + 1; j < k; j++)
                            b[j] = b[j - 1] + 1;
                        break;
                    }
                    mx = b[ii] - 1;
                }
            }
            return resList;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            //Comb cb = new Comb();
            /*for (double mx = 1.0; mx <= 100; mx++)
            {
                double pro = 1;
                for (double i = 1.0; i <= mx; i += 1.0)
                    pro *= (1.0 - (i / 365.0));
                Console.WriteLine($"{mx}: {1-pro}");

            }*/
            /*int i = 0;
            foreach(var item in Comb.SubSetsGeneration(new int[] { 1, 2, 3, 4, 5}))
                Console.WriteLine("{0}: {1}", ++i, String.Join(", ", item));
            */
            /*int j = 0;
            foreach (var item in Comb.RepetitionPlacing(new int[] { 1, 2, 3, 4, 5 }, 2).OrderBy(el => el.Count()))
                Console.WriteLine("{0}: {1}", ++j, String.Join(", ", item));*/

            int k = 0;
            foreach (var item in Comb.Combinations(new int[] { 1, 2, 3, 4, 5 }, 4).OrderBy(el => el.Count()))
                Console.WriteLine("{0}: {1}", ++k, String.Join(", ", item));


            //Console.WriteLine(cb.ToString());
        }
    }
}