c++ - 陈述/计算的生日悖论

Question

显然，我实际上是想创建一个数组，在多次试验 (5000) 中随机分配生日。然后假设每次有 2 - 50 人至少有 2 个生日时，将结果除以 5,000 以获得近似概率。我相信我的循环搞砸了，希望得到一些反馈。不是代码，我想确切地了解出了什么问题以及我是如何搞砸的。

int main()
{
    const int trials(5000);
    double total;
    int count(0), birthdays[49];

    srand(time(NULL));

    for (int i = 2; i <= 50; i++)
    {
        for (int k = 0; k < trials; k++)
        {
            fillUp(birthdays, 49);
            for (int j = i + 1; j <= 50; j++)
            {
                if (birthdays[i] == birthdays[j])
                {
                    count += 1;
                }
            }
        }
        total = count / 5000.0;
        cout << "For " << i << " the probability is " << total << endl;
    }
    return 0;
}

void fillUp(int birthdays [], int size)
{
    for (int i = 0; i < size; i++)
    {
        birthdays[i] = rand() % 365 + 1;
    }
}

输出:

For 2 the probability is 0.1286
For 3 the probability is 0.2604
...
...
For 49 the probability is 3.9424
For 50 the probability is 3.9424

非常感谢任何帮助。

Answer 1

问题不在于 C++ 代码；你只是在数学上打错了字。应该是:

power = (num * (num - 1.0) / 2.0);
chance = 1.0 - pow(constant, power);