代码实现排列组合【Java】

一.代码实现　　

 package zhen;

 import java.util.Arrays;

 public class Arrangement {

       /**
      * 计算阶乘数，即n! = n * (n-1) * ... * 2 * 1
      */
     private static long factorial(int n) {
         long sum = 1;
         while( n > 0 ) {
             sum = sum * n--;
         }
         return sum;
     }

       /**
      * 排列计算公式A = n!/(n - m)!
      */
     public static long arrangement(int m, int n) {
         return m <= n ? factorial(n) / factorial(n - m) : 0;
     }

      /**
      * 排列选择（从列表中选择n个排列）
      * @param dataList 待选列表
      * @param n 选择个数
      */
     public static void arrangementSelect(String[] dataList, int n) {
         System.out.println(String.format("A(%d, %d) = %d", dataList.length, n, arrangement(n, dataList.length)));
         arrangementSelect(dataList, new String[n], 0);
     }

     /**
      * 排列选择
      * @param dataList 待选列表
      * @param resultList 前面（resultIndex-1）个的排列结果
      * @param resultIndex 选择索引，从0开始
      */
     private static void arrangementSelect(String[] dataList, String[] resultList, int resultIndex) {
         int resultLen = resultList.length;
         if(resultIndex >= resultLen) { // 全部选择完时，输出排列结果
             System.out.println(Arrays.asList(resultList));
             return;
         }

         // 递归选择下一个
         for(int i = 0; i < dataList.length; i++) {
             // 判断待选项是否存在于排列结果中
             boolean exists = false;
             for (int j = 0; j < resultIndex; j++) {
                 if (dataList[i].equals(resultList[j])) {
                     exists = true;
                     break;
                 }
             }
             if (!exists) { // 排列结果不存在该项，才可选择
                 resultList[resultIndex] = dataList[i];
                 arrangementSelect(dataList, resultList, resultIndex + 1);
             }
         }
     }

     /**
      * 组合计算公式C<sup>m</sup><sub>n</sub> = n! / (m! * (n - m)!)
      * @param m
      * @param n
      * @return
      */
     public static long combination(int m, int n) {
         return m <= n ? factorial(n) / (factorial(m) * factorial((n - m))) : 0;
     }

     /**
      * 组合选择（从列表中选择n个组合）
      * @param dataList 待选列表
      * @param n 选择个数
      */
     public static void combinationSelect(String[] dataList, int n) {
         System.out.println(String.format("C(%d, %d) = %d", dataList.length, n, combination(n, dataList.length)));
         combinationSelect(dataList, 0, new String[n], 0);
     }

     /**
      * 组合选择
      * @param dataList 待选列表
      * @param dataIndex 待选开始索引
      * @param resultList 前面（resultIndex-1）个的组合结果
      * @param resultIndex 选择索引，从0开始
      */
     private static void combinationSelect(String[] dataList, int dataIndex, String[] resultList, int resultIndex) {
         int resultLen = resultList.length;
         int resultCount = resultIndex + 1;
         if (resultCount > resultLen) { // 全部选择完时，输出组合结果
             System.out.println(Arrays.asList(resultList));
             return;
         }

         // 递归选择下一个
         for (int i = dataIndex; i < dataList.length + resultCount - resultLen; i++) {
             resultList[resultIndex] = dataList[i];
             combinationSelect(dataList, i + 1, resultList, resultIndex + 1);
         }
     }

     public static void main(String[] args) {
         String[] array = new String[4];

         array[0] = "SG614111010000000010001";
         array[1] = "SG614111020000000020001";
         array[2] = "SG614111030000000030001";
         array[3] = "SG614111040000000040001";
         /**
          * 测试排列
          */
         System.out.println("测试排列：");
         arrangementSelect(array, array.length);

         /**
          * 测试组合
          */
         System.out.println("测试组合：");
         for(int i = 1; i <= array.length; i++){
             combinationSelect(array, i);
         }
     }
 }

二.结果

 测试排列：
 A(4, 4) = 24
 [SG614111010000000010001, SG614111020000000020001, SG614111030000000030001, SG614111040000000040001]
 [SG614111010000000010001, SG614111020000000020001, SG614111040000000040001, SG614111030000000030001]
 [SG614111010000000010001, SG614111030000000030001, SG614111020000000020001, SG614111040000000040001]
 [SG614111010000000010001, SG614111030000000030001, SG614111040000000040001, SG614111020000000020001]
 [SG614111010000000010001, SG614111040000000040001, SG614111020000000020001, SG614111030000000030001]
 [SG614111010000000010001, SG614111040000000040001, SG614111030000000030001, SG614111020000000020001]
 [SG614111020000000020001, SG614111010000000010001, SG614111030000000030001, SG614111040000000040001]
 [SG614111020000000020001, SG614111010000000010001, SG614111040000000040001, SG614111030000000030001]
 [SG614111020000000020001, SG614111030000000030001, SG614111010000000010001, SG614111040000000040001]
 [SG614111020000000020001, SG614111030000000030001, SG614111040000000040001, SG614111010000000010001]
 [SG614111020000000020001, SG614111040000000040001, SG614111010000000010001, SG614111030000000030001]
 [SG614111020000000020001, SG614111040000000040001, SG614111030000000030001, SG614111010000000010001]
 [SG614111030000000030001, SG614111010000000010001, SG614111020000000020001, SG614111040000000040001]
 [SG614111030000000030001, SG614111010000000010001, SG614111040000000040001, SG614111020000000020001]
 [SG614111030000000030001, SG614111020000000020001, SG614111010000000010001, SG614111040000000040001]
 [SG614111030000000030001, SG614111020000000020001, SG614111040000000040001, SG614111010000000010001]
 [SG614111030000000030001, SG614111040000000040001, SG614111010000000010001, SG614111020000000020001]
 [SG614111030000000030001, SG614111040000000040001, SG614111020000000020001, SG614111010000000010001]
 [SG614111040000000040001, SG614111010000000010001, SG614111020000000020001, SG614111030000000030001]
 [SG614111040000000040001, SG614111010000000010001, SG614111030000000030001, SG614111020000000020001]
 [SG614111040000000040001, SG614111020000000020001, SG614111010000000010001, SG614111030000000030001]
 [SG614111040000000040001, SG614111020000000020001, SG614111030000000030001, SG614111010000000010001]
 [SG614111040000000040001, SG614111030000000030001, SG614111010000000010001, SG614111020000000020001]
 [SG614111040000000040001, SG614111030000000030001, SG614111020000000020001, SG614111010000000010001]
 测试组合：
 C(4, 1) = 4
 [SG614111010000000010001]
 [SG614111020000000020001]
 [SG614111030000000030001]
 [SG614111040000000040001]
 C(4, 2) = 6
 [SG614111010000000010001, SG614111020000000020001]
 [SG614111010000000010001, SG614111030000000030001]
 [SG614111010000000010001, SG614111040000000040001]
 [SG614111020000000020001, SG614111030000000030001]
 [SG614111020000000020001, SG614111040000000040001]
 [SG614111030000000030001, SG614111040000000040001]
 C(4, 3) = 4
 [SG614111010000000010001, SG614111020000000020001, SG614111030000000030001]
 [SG614111010000000010001, SG614111020000000020001, SG614111040000000040001]
 [SG614111010000000010001, SG614111030000000030001, SG614111040000000040001]
 [SG614111020000000020001, SG614111030000000030001, SG614111040000000040001]
 C(4, 4) = 1
 [SG614111010000000010001, SG614111020000000020001, SG614111030000000030001, SG614111040000000040001]