public class PermutationAndCombination<T>
 {
 /// <summary>
 /// 交換兩個變量
 /// </summary>
 /// <param name="a">變量1</param>
 /// <param name="b">變量2</param>
 public static void Swap(ref T a, ref T b)
 {
 T temp = a;
 a = b;
 b = temp;
 }
 /// <summary>
 /// 遞歸算法求數(shù)組的組合(私有成員)
 /// </summary>
 /// <param name="list">返回的范型</param>
 /// <param name="t">所求數(shù)組</param>
 /// <param name="n">輔助變量</param>
 /// <param name="m">輔助變量</param>
 /// <param name="b">輔助數(shù)組</param>
 /// <param name="M">輔助變量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>
 /// 遞歸算法求排列(私有成員)
 /// </summary>
 /// <param name="list">返回的列表</param>
 /// <param name="t">所求數(shù)組</param>
 /// <param name="startIndex">起始標號</param>
 /// <param name="endIndex">結(jié)束標號</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>
 /// 求從起始標號到結(jié)束標號的排列，其余元素不變
 /// </summary>
 /// <param name="t">所求數(shù)組</param>
 /// <param name="startIndex">起始標號</param>
 /// <param name="endIndex">結(jié)束標號</param>
 /// <returns>從起始標號到結(jié)束標號排列的范型</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>
 /// 返回數(shù)組所有元素的全排列
 /// </summary>
 /// <param name="t">所求數(shù)組</param>
 /// <returns>全排列的范型</returns>
 public static List<T[]> GetPermutation(T[] t)
 {
 return GetPermutation(t, 0, t.Length - 1);
 }
 /// <summary>
 /// 求數(shù)組中n個元素的排列
 /// </summary>
 /// <param name="t">所求數(shù)組</param>
 /// <param name="n">元素個數(shù)</param>
 /// <returns>數(shù)組中n個元素的排列</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>
 /// 求數(shù)組中n個元素的組合
 /// </summary>
 /// <param name="t">所求數(shù)組</param>
 /// <param name="n">元素個數(shù)</param>
 /// <returns>數(shù)組中n個元素的組合的范型</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;
 }
 }

求組合：求5個數(shù)里任意3個數(shù)的組合

 static void Main(string[] args)
 {
 int[] IntArr = new int[] { 1, 2, 3, 4, 5 }; //整型數(shù)組
 List<int[]> ListCombination = PermutationAndCombination<int>.GetCombination(IntArr, 3); //求全部的3-3組合
 foreach(int[] arr in ListCombination)
 {
 foreach(int item in arr)
 {
 Console.Write(item + " ");
 }
 Console.WriteLine("");
 }
 Console.ReadKey();
 }

求排列：5個數(shù)取3個的任意排列

 int[] IntArr = new int[] { 1, 2, 3, 4, 5 }; //整型數(shù)組
 List<int[]> ListCombination = PermutationAndCombination<int>.GetPermutation(IntArr, 3); //求全部的5取3排列
 foreach(int[] arr in ListCombination)
 {
 foreach(int item in arr)
 {
 Console.Write(item + " ");
 }
 Console.WriteLine("");
 }