partial_random_shuffle.cpp

partial_random_shuffle.cpp

#include <algorithm>
#include <random>
#include <iostream>
using namespace std;

template< class RandomIt>
void partial_random_shuffle( RandomIt first, RandomIt last,  RandomIt part) {
    typename std::iterator_traits<RandomIt>::difference_type i, n, p;
    p = part - first;
    n = last - first;
    std::uniform_int_distribution<> dist(0, n - 1);
    std::random_device rd;
    std::default_random_engine rng {rd()};
    for (i = 0; i < p; i ++ ) {
        std::swap(first[i], first[dist(rng)]);
    }
}

int main() {
    std::vector<int> v(100000);
    for (size_t i = 0; i < v.size(); i++) {
        v[i] = int(i);
    }
    partial_random_shuffle(v.begin(), v.end(), v.begin() + 100);
    for (int i = 0; i < 100; i++) {
        cout << v[i] << endl;
    }
}