使用给定的随机生成器函数从1到7生成随机数

Question

使用函数以相等的概率随机生成数字1到5，并以相同的概率创建一个函数，该函数以相等的概率生成数字1到7。

我修改了以前的答案之一。这是对的吗？

#include <bits/stdc++.h> 
#define ran rand()%5 
using namespace std; 
int main(){ 
    int a[2][5] = {{1, 2, 3, 4, 5}, {6, 7, 0, 0, 0}}; 
    int ct[8] = {0}; 
    for(int i = 0; i<50000000; i++){ 
     int j = ran; 
     while(j>1){ 
      j = ran; 
     } 
     int k = ran; 
     if(a[j][k]>0) 
      ct[a[j][k]]++; 
    } 

    for(int i = 1; i<=7; i++){ 
     cout<<ct[i]<<endl; 
    } 
    return 0; 
} 

我有以下的输出：

4997165 
4998128 
4997312 
5002487 
5000661 
4998637 
4999720 

请告诉我们，如果有什么不对的地方。

Answer 1

这里是一个现代化的C++解决方案：

#include <algorithm> 
#include <functional> 
#include <iostream> 
#include <iterator> 
#include <ostream> 
#include <random> 

template <unsigned int Min, unsigned int Max> 
class imbued_urng 
{ 
public: 
    using result_type = unsigned int; 

    static constexpr result_type min() { return Min; } 
    static constexpr result_type max() { return Max; } 

    imbued_urng(const std::function<result_type()>& source) : random{ source } {} 
    imbued_urng(const imbued_urng& rhs) = delete; 
    imbued_urng& operator=(const imbued_urng& rhs) = delete; 

    result_type operator()() { return random(); } 

private: 
    const std::function<result_type()>& random; 
}; 

int main() 
{ 
    // Create a random number engine 
    std::mt19937::result_type seed = std::random_device{}(); 
    std::cout << "seed = " << seed << std::endl; 
    auto engine = std::mt19937{ seed }; 

    // Create the rand5 distribution 
    auto const dist5{ std::uniform_int_distribution<> {1, 5} }; 
    auto const rand5{ std::function<unsigned int()>{ [&engine, &dist5] { return dist5(engine); } } }; 

    auto const n = 32; 
    std::generate_n(std::ostream_iterator<unsigned int>(std::cout, " "), n, rand5); 
    std::cout << std::endl; 

    // Create a uniform random number generator based on rand5 
    imbued_urng<1, 5> urng { rand5 }; 

    // Create the rand7 distribution 
    auto const dist7{ std::uniform_int_distribution<> {1, 7} }; 
    auto const rand7{ std::function<unsigned int()>{ [&urng, &dist7] { return dist7(urng); } } }; 

    std::generate_n(std::ostream_iterator<unsigned int>(std::cout, " "), n, rand7); 
    std::cout << std::endl; 

    return 0; 
}