【Java】将字符串随机乱序的三函数

要将字符串乱序输出，一种思路是使用Collections.shuffle(),一种思路是自己写随机置换函数。

但将原文转列表也有开销，它和置换函数谁更快了，还是让实验说话。

经实践证明，凡是字符串操作能走char数组下标置换的的尽量走下标，转list用正则等效率就下去了。

 

代码如下：

package com.hy.lab.shuffle;

import java.util.*;

public class Test {
    // 低效
    public static String shuffle1(String original){
        List list = Arrays.asList(original.split(""));
        Collections.shuffle(list);
        StringBuilder sb=new StringBuilder();
        list.forEach(item->sb.append(item));
        return sb.toString();
    }

    // 居中，约为shuffle1的一半时间
    public static String shuffle2(String original){
        List<Character> list=new ArrayList<>();
        char[] arr=original.toCharArray();
        for(char c:arr){
            list.add(c);
        }

        Collections.shuffle(list);
        StringBuilder sb=new StringBuilder();
        list.forEach(item->sb.append(item));
        return sb.toString();
    }

    // 高效，约为shuffle1的一成时间
    public static String shuffle3(String original){
        char[] arr=original.toCharArray();
        Random rnd=new Random();
        char tmp;
        int j;

        for(int i=arr.length;i>1;i--){
            j=rnd.nextInt(i);
            tmp=arr[i-1];
            arr[i-1]=arr[j];
            arr[j]=tmp;
        }

        return String.valueOf(arr);
    }

    private static int rnd(int min,int max) {
        return (int)(min+Math.random()*(max-min+1));
    }

    public static void main(String[] args){
        System.out.println(shuffle1("abcdefghijklmnopqrstuvwxyz"));
        System.out.println(shuffle2("ABCDEFGHIJKLMNOPQRSTUVWXYZ"));
        System.out.println(shuffle3("0123456789"));

        long startMs=System.currentTimeMillis();
        for(int i=0;i<100000;i++) {
            shuffle1("abcdefghijklmnopqrstuvwxyz");
        }
        long endMs=System.currentTimeMillis();
        System.out.println("shuffle耗时:"+ms2DHMS(startMs,endMs));

        startMs=System.currentTimeMillis();
        for(int i=0;i<100000;i++) {
            shuffle2("abcdefghijklmnopqrstuvwxyz");
        }
        endMs=System.currentTimeMillis();
        System.out.println("shuffle2耗时:"+ms2DHMS(startMs,endMs));

        startMs=System.currentTimeMillis();
        for(int i=0;i<100000;i++) {
            shuffle3("abcdefghijklmnopqrstuvwxyz");
        }
        endMs=System.currentTimeMillis();
        System.out.println("shuffle3耗时:"+ms2DHMS(startMs,endMs));
    }

    private static String ms2DHMS(long startMs, long endMs) {
        String retval = null;
        long secondCount = (endMs - startMs) / 1000;
        String ms = (endMs - startMs) % 1000 + "ms";

        long days = secondCount / (60 * 60 * 24);
        long hours = (secondCount % (60 * 60 * 24)) / (60 * 60);
        long minutes = (secondCount % (60 * 60)) / 60;
        long seconds = secondCount % 60;

        if (days > 0) {
            retval = days + "d" + hours + "h" + minutes + "m" + seconds + "s";
        } else if (hours > 0) {
            retval = hours + "h" + minutes + "m" + seconds + "s";
        } else if (minutes > 0) {
            retval = minutes + "m" + seconds + "s";
        } else if(seconds > 0) {
            retval = seconds + "s";
        }else {
            return ms;
        }

        return retval + ms;
    }
}

 

输出：

irsyoanjucwfzxkvhelgpdbqtm
RJECQGFPKNXTSVHOWDIMUBZAYL
4137960528
shuffle耗时:1s32ms
shuffle2耗时:359ms
shuffle3耗时:78ms

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