c++ partial_shuffle

main.cpp

#include <iostream>
#include <cstring>
#include <random>
#include <chrono>
#include <iterator>

template<class RandomIt, class URBG>
void partial_shuffle(RandomIt first, RandomIt middle, RandomIt last, URBG&& g)
{
	using difference_type = typename std::iterator_traits<RandomIt>::difference_type;
	using value_type = typename std::make_unsigned<difference_type>::type;
	using distribution_type = std::uniform_int_distribution<value_type>;
	using param_type = typename distribution_type::param_type;

	if (first == middle)
		return;

	distribution_type d;

	for (auto it = first; it != middle; ++it) {
		std::iter_swap(it, first + d(g, param_type(it - first, last - first - 1)));
	}
}

int main(int argc, char** argv) {
	std::random_device rd;
	const int x[] = {0,1,2,3,4,5,6,7,8,9};
	int z[10];
	int p[10][10];

	std::memset(p, 0, sizeof(p));

	for (int i = 0; i < 1000000; i++) {
		std::copy(x, x+sizeof(x)/sizeof(x[0]), z);
		partial_shuffle(z, z+3, z+sizeof(z)/sizeof(z[0]), rd);

		for (int j = 0; j < 10; j++) {
			p[j][z[j]]++;
		}
	}

	for (int j = 0; j < 10; j++) {
		for (int i = 0; i < 10; i++) {
			std::cout << p[j][i] << " ";
		}
		std::cout << std::endl;
	}


	return 0;
}