Java练习题-输入一个字符串，输出该字符串中字符的所有组合（一）

import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

/**
 * 输入一个字符串，输出该字符串中字符的所有组合，组合中不能出现重复的字符。
 * 如：
 * abc ==> a、b、c、ab、ac、ba、bc、ca、cb、abc、acb、bac、bca、cab、cba
 * 
 * @author tang
 *
 */
public class Test {

    public static void main(String[] args) {
        List list = getResultList("12345");
        System.out.println(list);
    }

    public static List getResultList(String s) {
        HashSet set = new HashSet();
        traverseCharArray(s.toCharArray(), set);
        List list = new LinkedList(set);
        Collections.sort(list, new Comparator() {
            public int compare(String o1, String o2) {
                if (o1.length() == o2.length()) {
                    return o1.compareToIgnoreCase(o2);
                } else {
                    return o1.length() - o2.length();
                }
            }
        });
        return list;
    }

    public static void traverseCharArray(char[] chars, HashSet set) {
        for (int i = 0; i < chars.length; i++) {
            recursionMerge(chars[i], getOther(chars, i), set);
        }
    }

    public static Set recursionMerge(char c, char[] chars, HashSet set) {
        Set merges = new HashSet();
        String merge = merge(c + "", new String(chars));
        merges.add(merge);
        set.add(merge);

        for (int i = 0; i < chars.length; i++) {
            Set mergeSet = recursionMerge(chars[i], getOther(chars, i), set);
            for (String str : mergeSet) {
                String merge2 = merge(c + "", str);
                set.add(merge2);
                merges.add(merge2);
            }
        }
        return merges;
    }

    public static char[] getOther(char[] c1, int index) {
        StringBuffer buffer = new StringBuffer(new String(c1));
        buffer.deleteCharAt(index);
        return buffer.toString().toCharArray();
    }

    public static String merge(String s1, String s2) {
        return s1 + s2;
    }
}