字母全排列

小咪咪 2022-04-10 01:55 180阅读 0赞

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);
            }
        }
    
    }