字母全排列

package com.jf.wwsh.test;


import java.util.ArrayList;
import java.util.List;

/**
 * 描述:
 *
 * @author fengyong
 * @date 2018/11/30.
 */
public class MainTest {
    public static void main(String[] args) {
        char[] chs1 = {\'a\',\'b\',\'c\',\'d\',\'e\',\'f\',\'g\',\'h\',\'i\',\'j\',\'k\',\'l\',\'m\',\'n\',\'o\',\'p\',\'q\',\'r\',\'s\',\'t\',\'u\',\'v\',\'w\',\'x\',\'y\',\'z\'};
        char[] chs = {\'a\',\'b\',\'c\',\'d\'};
        long startTime=System.currentTimeMillis();
        comb(chs);
        long endTime=System.currentTimeMillis();
        System.out.println(\"当前程序耗时：\"+(endTime-startTime)+\"ms\");
    }

    public static void comb(char[] chs) {
        int len = chs.length;
        int nbits = 1 << len;
        List<List<Character>> list1 = new ArrayList<>();
        for (int i = 0; i < nbits; ++i) {
            List<Character> list2 = new ArrayList<>();
            int t;
            for (int j = 0; j < len; j++) {
                t = 1 << j;
                if ((t & i) != 0) { // 与运算，同为1时才会是1
                    list2.add(chs[j]);
                }
            }
            list1.add(list2);
        }
        list1.remove(0);
        for(List<Character> characters:list1){
            Character[] chs1 = characters.toArray(new Character[characters.size()]);
            per(new char[characters.size()],chs1,characters.size()-1);
        }
        System.out.println(list3.size());
    }
    static List<List<Character>> list3 = new ArrayList<>();

    public static void per(char[] buf, Character[] chs, int len){
        if(len == -1){
            List<Character> list4 = new ArrayList<>();
            for(int i=buf.length-1; i>=0; --i){
                //System.out.print(buf[i]);
                list4.add(buf[i]);
            }
            //System.out.println();
            list3.add(list4);
            return;
        }
        for(int i=0; i<chs.length; i++){
            buf[len] = chs[i];
            per(buf, chs, len-1);
        }
    }

}