C#泛型排列组合核心算法

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace calu
{
    class Program
    {
        static void Main(string[] args)
        {
            float[] arr = new float[3];
            for (int i = 0; i < arr.Length; i++)
            {
                arr[i] = i + 1;
            }
            //求排列
            List<float[]> lst_Permutation = PermutationAndCombination<float>.GetPermutation(arr,3);
            //其中
            List<float[]> lst_Combination = PermutationAndCombination<float>.GetCombination(arr, 2);
            Console.WriteLine("排列:");
            int icount = 1;
            foreach (float[] array in lst_Permutation)
            {                
                Console.Write("排列1" + icount++ + "-->");
                foreach (float itemp in array)
                {
                    Console.Write(itemp.ToString() + ",");
                }
                Console.WriteLine();               
            }
            Console.WriteLine("组合:");
            icount = 1;
            foreach (float[] array in lst_Combination)
            {
                Console.Write("组合1" + icount++ + "-->");
                foreach (float itemp in array)
                {
                    Console.Write(itemp.ToString() + ",");
                }
                Console.WriteLine();
            }
            Console.ReadKey();

        }
        /// <summary>
        /// 排列组合算法
        /// </summary>
        /// <typeparam name="T"></typeparam>
        public static class PermutationAndCombination<T>
        {
            /// <summary>
            /// 交换两个变量
            /// </summary>
            /// <param name="a">变量1</param>
            /// <param name="b">变量2</param>
            public static void Swap(ref T a, ref T b)
            {
                T temp = a;
                a = b;
                b = temp;
            }

            /// <summary>
            /// 递归算法求数组的组合(私有成员)，核心算法
            /// </summary>
            /// <param name="list">返回的范型</param>
            /// <param name="t">所求数组</param>
            /// <param name="n">辅助变量</param>
            /// <param name="m">辅助变量</param>
            /// <param name="b">辅助数组</param>
            /// <param name="M">辅助变量M</param>
            private static void GetCombination(ref List<T[]> list, T[] t, int n, int m, int[] b, int M)
            {
                for (int i = n; i >= m; i--)
                {
                    b[m - 1] = i - 1;
                    if (m > 1)
                    {
                        GetCombination(ref list, t, i - 1, m - 1, b, M);
                    }
                    else
                    {
                        if (list == null)
                        {
                            list = new List<T[]>();
                        }
                        T[] temp = new T[M];
                        for (int j = 0; j < b.Length; j++)
                        {
                            temp[j] = t[b[j]];
                        }
                        list.Add(temp);
                    }
                }
            }

            /// <summary>
            /// 递归算法求排列(私有成员)，核心算
            /// </summary>
            /// <param name="list">返回的列表</param>
            /// <param name="t">所求数组</param>
            /// <param name="startIndex">起始标号</param>
            /// <param name="endIndex">结束标号</param>
            private static void GetPermutation(ref List<T[]> list, T[] t, int startIndex, int endIndex)
            {
                if (startIndex == endIndex)//只有一种方法
                {
                    if (list == null)
                    {
                        list = new List<T[]>();
                    }
                    T[] temp = new T[t.Length];
                    t.CopyTo(temp, 0);
                    list.Add(temp);
                }
                else
                {
                    for (int i = startIndex; i <= endIndex; i++)
                    {
                        Swap(ref t[startIndex], ref t[i]);
                        GetPermutation(ref list, t, startIndex + 1, endIndex);
                        Swap(ref t[startIndex], ref t[i]);
                    }
                }
            }

            /// <summary>
            /// 求从起始标号到结束标号的排列，其余元素不变
            /// </summary>
            /// <param name="t">所求数组</param>
            /// <param name="startIndex">起始标号</param>
            /// <param name="endIndex">结束标号</param>
            /// <returns>从起始标号到结束标号排列的范型</returns>
            public static List<T[]> GetPermutation(T[] t, int startIndex, int endIndex)
            {
                if (startIndex < 0 || endIndex > t.Length - 1)
                {
                    return null;
                }
                List<T[]> list = new List<T[]>();
                GetPermutation(ref list, t, startIndex, endIndex);
                return list;
            }

            /// <summary>
            /// 返回数组所有元素的全排列
            /// </summary>
            /// <param name="t">所求数组</param>
            /// <returns>全排列的范型</returns>
            public static List<T[]> GetPermutation(T[] t)
            {
                return GetPermutation(t, 0, t.Length - 1);
            }

            /// <summary>
            /// 求数组中n个元素的排列
            /// </summary>
            /// <param name="t">所求数组</param>
            /// <param name="n">元素个数</param>
            /// <returns>数组中n个元素的排列</returns>
            public static List<T[]> GetPermutation(T[] t, int n)
            {
                if (n > t.Length)
                {
                    return null;
                }
                List<T[]> list = new List<T[]>();
                List<T[]> c = GetCombination(t, n);
                for (int i = 0; i < c.Count; i++)
                {
                    List<T[]> l = new List<T[]>();
                    GetPermutation(ref l, c[i], 0, n - 1);
                    list.AddRange(l);
                }
                return list;
            }

            /// <summary>
            /// 求数组中n个元素的组合
            /// </summary>
            /// <param name="t">所求数组</param>
            /// <param name="n">元素个数</param>
            /// <returns>数组中n个元素的组合的范型</returns>
            public static List<T[]> GetCombination(T[] t, int n)
            {
                if (t.Length < n)
                {
                    return null;
                }
                int[] temp = new int[n];
                List<T[]> list = new List<T[]>();
                GetCombination(ref list, t, t.Length, n, temp, n);
                return list;
            }
        }

    }
}