生成随机数

打乱数组中的内容

参考1

参考2

目前我用到的是std::shuffle_order_engine.功能是打乱数组中的内容

random功能主要由两个部分组成：generators和distribution(不一定用分布)

generators
a.Pseudo-random（伪随机数） number engines (templates)
b. Engine adaptors
- independent_bits_engine
- shuffle_order_engine
c. 伪随机数引擎(实例化)
d.随机数生成器

random_device
distributions
Uniform:
- uniform_int_distribution
- uniform_real_distribution
  Related to Bernoulli (yes/no) trials:
- bernoulli_distribution
- binomial_distribution
- geometric_distribution
- negative_binomial_distribution
  Rate-based distributions:
- poisson_distribution
- exponential_distribution
- gamma_distribution
- weibull_distribution
- extreme_value_distribution
  Related to Normal distribution:
- normal_distribution
- lognormal_distribution
- chi_squared_distribution
- cauchy_distribution
- fisher_f_distribution
- student_t_distribution
  Piecewise distributions:
- discrete_distribution
- piecewise_constant_distribution
- piecewise_linear_distribution

实例1：

#include <iostream>
#include <algorithm>
#include <random>
#include <functional>
#include <chrono> // std::chrono::system_clock
//refernce:http://www.cplusplus.com/reference/random/

int main(_In_ int _Argc, _In_reads_(_Argc) _Pre_z_ char ** _Argv, _In_z_ char ** _Env)
{
	//该seed使得每次运行的结果都不同
    //用时间作为seed或者随机数生成器作为seed
	unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
    std::default_random_engine generator(seed);
	std::uniform_int_distribution<int> distribution(1, 6);
	// generates number in the range 1..6 
	for (size_t i = 0; i < 10; i++)
	{
		int dice_roll = distribution(generator);
		std::cout << dice_roll << " ";
	}
	std::cout << std::endl;
	//为了重复使用将两着绑定在一起
	auto dice = std::bind(distribution, generator);

	for (size_t i = 0; i < 10; i++)
	{
		int wisdom = dice() + dice() + dice();
		std::cout << wisdom << " ";
	}
	getchar();
	return 0;
}

输出：

3 1 3 6 5 2 6 6 1 2
9 8 11 13 9 12 12 9 5 9

实例2：（使用Engine adaptors：shuffle打乱vector顺序）

#include <iostream>
#include <vector>
#include <algorithm> // std::move_backward
#include <random> // std::default_random_engine
#include <chrono> // std::chrono::system_clock

int main(int argc, char* argv[])
{
	std::vector<int> v;

	for (int i = 0; i < 10; ++i) {
		v.push_back(i);
	}

	// obtain a time-based seed:
	//unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
	//std::shuffle(v.begin(), v.end(), std::default_random_engine(seed));
    //或者用随机数生成器
    std::random_device rand_dev;
	std::shuffle(v.begin(), v.end(), std::default_random_engine(rand_dev()));

	for (auto& it : v) {
		std::cout << it << " ";
	}

	std::cout << "\n";
	getchar();
	return 0;
}

输出：

9 1 4 6 2 7 0 5 3 8

# C++, STL, std

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