求字符串的len组合数（java程序）

import java.util.List;import java.util.ArrayList;/** * 求字符串的len组合数 * * @author wenin819 * */public class Combination{/** * 求组合数的主要方法 */public static List<String> combination(String inStr, int len){StringBuffer noDoubleStr =new StringBuffer(inStr);noDouble(noDoubleStr);if( len >= noDoubleStr.length()) return null;return combinationItem(noDoubleStr , len);}/** * 去除重复的字符 */public static void noDouble(StringBuffer input){for(int i = 0; i < input.length(); i++){char temp = input.charAt(i);for(int j = i+1; j < input.length(); ){if(temp == input.charAt(j)){input.deleteCharAt(j);}else{j++;}}}}/** * 求组合数 */public static List<String> combinationItem(StringBuffer input, int len){List<String> rsList = new ArrayList<String>();boolean[] array = new boolean[input.length()];for(int i = 0; i < array.length; i++){array[i] = false;}do{if(len == countOfTrue(array)){StringBuffer temp = new StringBuffer(input);for(int j = temp.length() - 1;j >= 0;j--){if(array[j]) continue;temp.deleteCharAt(j);}rsList.add(new String(temp));}}while(booleanAdd(array));return rsList;}/** * 求boolean数组元素为true的个数 */public static int countOfTrue(boolean[] array){int count = 0;for(int i = 0;i < array.length;i++){if(array[i]) count++;}return count;}/** * boolean数组自加（同2进制加1） */public static boolean booleanAdd(boolean[] array){boolean flag = true;for(int i = 0;i < array.length; i++){if(false == flag) return true;if(array.length-1 == i && true == array[i]){array[i] = false;return false;}if(false == array[i]){array[i] = true;return true;}array[i] = false;}return false;}public static void main(String[] args){String input = new String("abcde");int len = 3;if(args.length > 1){input = args[0];len = Integer.parseInt(args[1]);}List list = combination(input,len);if(list != null){System.out.println(input+"的"+len+"组合数的个数为："+list.size()+"/n组合数分别为：");for(int i = 0; i < list.size(); i++){System.out.println(i+1+": "+list.get(i).toString());}}}}