randM()到randN()

最新推荐文章于 2024-05-03 16:14:54 发布

hanbingsqq

最新推荐文章于 2024-05-03 16:14:54 发布

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分类专栏：算法

本文链接：https://blog.youkuaiyun.com/hanbingsqq/article/details/79630926

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本文探讨了如何将基本的随机数生成函数rand5()扩展到randN()，并通过rand01p()函数实现概率分布。首先介绍了如何使用rand5()模拟rand7()，接着阐述了rand01p()函数在概率分布中的应用，最后讲解了通用的randM()到randN()的转换方法。

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1、rand5()到rand7()

class Rand5To7
{
    public int rand5()
    {
        return (int) (Math.random() * 5) - 1;
    }
    public int rand5To7()
    {
        int num = 0;
        do{
            num = (rand5() - 1) * 5 + rand5() - 1;
        }while(num > 20);
        return num % 7 + 1;
    }
}

2、给定一个以p概率产生0，以1-p概率产生1的随机函数rand01p()

class Rand6
{
    public int rand01p()
    {
        double p = 0.80;
        return Math.random() < p ? 0 : 1;
    }
    public int rand01()
    {
        int num;
        do{
            num = rand01p();
        }while(num == rand01p());
        return num;
    }
    public int rand3()
    {
        return rand01() * 2 + rand01();
    }
    public int rand6()
    {
        int num = 0;
        do{
            num = rand3() * 4 + rand3();
        }while(num > 11);
        return num % 6 + 1;
    }
}

3、randM()到randN()

class randMToN
{
    public int randM(int m)
    {
        return (int) (Math.random() * m) + 1; 
    }
    public int randMToN(int m, int n)
    {
        int []nMNum = getnMNum(n-1, m);
        int []randMNum = getRandMNumLessN(nMNum, m);
        int res = getNumFromMNum(randMNum, m);
        return res;
    }
    public int[] getnMNum(int value, int m)
    {
        int []res = new int[32];
        int index = res.length - 1;
        while(value != 0)
        {
            res[index--] = value % m;
            value = value / m;
        }
        return res;
    }
    public int[] getRandMNumLessN(int []nMNum, int m)
    {
        int []res = new int[nMNum.length];
        int start = 0;
        while(nMNum[start] == 0) start++;
        int index = start;
        boolean lastEqual = true;
        while(index != nMNum.length)
        {
            res[index] = randM(m) - 1;
            if(lastEqual)
            {
                if(res[index] > nMNum[index])
                {
                    index = start;
                    lastEqual = true;
                    continue;
                }
                else
                {
                    lastEqual = res[index] == nMNum[index];
                }
            }
            index++;
        }
        return res;
    }
    public int getNumFromMNum(int []MNum, int m)
    {
        int res = 0;
        for(int i=0; i!=MNum.length; i++)
        {
            res = res * m + MNum[i];
        }
        return res;
    }
}