如何使用Java中的Math.random()以相等的概率生成随机数 [英] How do you generate a random number with equal probability using Math.random() in Java

问题描述

我目前正在练习中，我需要生成一个随机数，该随机数可以是4个值之一.(请注意，我只能使用Math.random())

I'm currently working through an exercise where I am required to generate a random number which can be one of 4 values. (note I'm only allowed to use Math.random())

01个2个或3

当前我正在使用: randno =(int)(Math.random()* 4);//范围为0-3

但是，结果必须具有相等的概率.到目前为止，我的测试(尽管缺少该方法)显示3出现的次数远少于其他数字.

However, the outcome MUST have equal probability. My tests so far (although the method is lacking) shows that 3 occurs far less than the other numbers.

这是巧合吗?还是我的发电机没有相等的概率.

Is this coincidence? Or does my generator not have equal probability.

谢谢！

推荐答案

您的代码运行良好:

   public static void main(String[] args) {

        int countZero = 0;
        int countOne = 0;
        int countTwo = 0;
        int countThree = 0;

        for(int i=0; i<400000; i++){            
            int randno =  (int)(Math.random() * ((3) + 1));

            if(randno == 0){
                countZero++;
            }
            else if(randno == 1){
                countOne++;
            }
            else if(randno == 2){
                countTwo++;
            }
            else if(randno == 3){
                countThree++;
            }           
        }

        System.out.println("Zero: " + countZero);
        System.out.println("One: " + countOne);
        System.out.println("Two: " + countTwo);
        System.out.println("Three: " + countThree);


    }

输出:

Zero: 99683
One: 99793
Two: 100386
Three: 100138

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