java實作全排列

面試的時候經常遇到“輸入一字元串，輸出字元串的所有排列”這道題目，今天我自己實作了一下，用的遞歸的思路。不多解釋，直接上代碼吧。

package test;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

/* 
 * 
 * 輸入一字元串，輸出字元串的所有排列
 */
public class PrintAllSequence {

    private static Set set = new HashSet<String>();
    private static int len = ;

    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");
        list.add("5");

        printAllSeq(list);

        System.out.println("共有" + set.size() + "種全排列");

        Iterator it = set.iterator();
        while(it.hasNext()){
            String s = (String) it.next();
            System.out.println(s);
        }
    }

    private static List<String> printAllSeq(List<String> list) {
        if (list.size() == ) {
            return list;
        }
        List<String> tempList = new ArrayList<String>();
        List<String> resultList = new ArrayList<String>();

        for (int i = ; i < list.size(); i++) {
            String prefix = list.get(i);
            list.remove(i);
            tempList = printAllSeq(list);
            for (int j = ; j < tempList.size(); j++) {
                String result = prefix + tempList.get(j);
                if(result.length() == len){
                    set.add(result);
                }
                resultList.add(result);
            }
            list.add(i, prefix);
        }
        return resultList;
    }
}