全排列和组合算法的C#语言实现
using System;namespace Util.Comp { public class CombinationPermutation { public static void Main() {//全排列使用方法 foreach(string s in Permutation(new string[] {"a", "b", "c"})){Console.WriteLine(s);}//组合使用方法foreach(string s in Combination(new string[] {"a","b","c"},2)){ Console.WriteLine(s); } } private static int Fac(int n) { int nRet = 1; for (int i = 2; i <= n; i++) nRet *= i; return nRet; } private static int CountC(int n, int r) { return Fac(n) / Fac(n - r) / Fac(r); } //全排列算法 public static string[] Permutation(string[] s) { int n = s.Length; int[] seq = new int[n]; for (int i = 0; i < n; i++) seq[i] = i; int[] a = new int[n]; for (int i = 0; i < n; i++) a[i] = seq[i]; int nCount = Fac(n); string[] ret_val = new string[nCount]; int index = 0; for (int i = 0; i < n; i++) { ret_val[index] += s[a[i]] + " "; } ret_val[index].TrimEnd(' '); index++; for (int k = 1; k < nCount; k++) { int m = n - 2; while (a[m] > a[m + 1]) m--; int q = n - 1; while (a[q] < a[m]) q--; int tmp; tmp = a[m]; a[m] = a[q]; a[q] = tmp; m = m + 1; q = n - 1; while (m < q) { tmp = a[m]; a[m] = a[q]; a[q] = tmp; q--; m++; } for (int i = 0; i < n; i++) { ret_val[index] += s[a[i]] + " "; } ret_val[index].TrimEnd(' '); index++; } return ret_val; } //组合算法public static string[] Combination(string[] seq, int n) { // 获得数组长度，判断组合参数的有效性 int m = seq.Length; if (m< 1 || n > m) return null; int i, index=0; int c = 1; // 组合的数目 // 计算组合的数目 for (i = 0; i < n; i++) c *= m - i; for(i=0;i<n;i++) c /= i+1; int[] a = new int[m]; string[] ret_val = new string[c]; // 保存组合的结果 // 将前n个元素初始化为1 for (i = 0; i < n; i++) a[i] = 1; // 输出第一个元素 for (int j = 0; j < n; j++) { ret_val[index] += seq[j] + " "; } ret_val[index].TrimEnd(' '); index++; int m_1 = m - 1; while(true){ // 寻找10 组合 int flag_found = 0; for (i = 0; i < m_1; i++) { if (a[i] == 1 && a[i + 1] == 0) { flag_found = 1; // 将10 改变成 01 a[i] = 0; a[i + 1] = 1; // 将左边的1都移动到最左边 int one_cnt = 0; for (int k = 0; k < i; k++) if (a[k] == 1) { a[k] = 0; a[one_cnt++] = 1; } // 输出一个组合 for (int j = 0; j < m; j++) if (a[j] == 1) ret_val[index] += seq[j] + " "; ret_val[index].TrimEnd(' '); index++; break; } } if (flag_found == 0) break; } return ret_val; } }}