详解C#的排列组合

public class PermutationAndCombination
 {
 /// 

 /// 交换两个变量
 /// 
 /// 变量1
 /// 变量2
 public static void Swap(ref T a, ref T b)
 {
 T temp = a;
 a = b;
 b = temp;
 }
 /// 

 /// 递归算法求数组的组合(私有成员)
 /// 
 /// 返回的范型
 /// 所求数组
 /// 辅助变量
 /// 辅助变量
 /// 辅助数组
 /// 辅助变量M
 private static void GetCombination(ref List 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[] temp = new T[M];
 for (int j = 0; j 
 /// 递归算法求排列(私有成员)
 /// 
 /// 返回的列表
 /// 所求数组
 /// 起始标号
 /// 结束标号
 private static void GetPermutation(ref List list, T[] t, int startIndex, int endIndex)
 {
 if (startIndex == endIndex)
 {
 if (list == null)
 {
 list = new List();
 }
 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]);
 }
 }
 }
 /// 

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

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

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

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

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

 int[] IntArr = new int[] { 1, 2, 3, 4, 5 }; //整型数组
 List ListCombination = PermutationAndCombination.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("");
 }