C# 写的 排列组合类

//-----------------------------------------------------------------------------

//

// 算法：排列组合类

//

//

// 调用方法如下：

//

// 1.GetPermutation(T[], startIndex, endIndex)

// 对startIndex到endIndex进行排列，其余元素不变

//

// 2.GetPermutation(T[])

// 返回数组所有元素的全排列

//

// 3.GetPermutation(T[], n)

// 返回数组中n个元素的排列

//

// 4.GetCombination(T[], n)

// 返回数组中n个元素的组合

//

// 版本历史：

// V0.1 2010-01-20   

//

//-----------------------------------------------------------------------------



using System;

using System.Collections.Generic;



namespace Algorithms

{

    public 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)

        /// </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)

        /// </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)

            {

                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;

        }

    }

}

调用：

int[] arr = new int[6];

for (int i = 0; i < arr.Length; i++)

{

    arr[i] = i + 1;

}

//求排列

List<int[]> lst_Permutation = Algorithms.PermutationAndCombination<int>.GetPermutation(arr, 3);

//求组合

List<int[]> lst_Combination = Algorithms.PermutationAndCombination<int>.GetCombination(arr, 3);