template<class OutputIter, class Size, class Generator>
constexpr OutputIter generate_n(OutputIter first, Size n, Generator gen);

template<class ExecutionPolicy, class ForwardIter, class Size, class Generator>
ForwardIter generate_n(ExecutionPolicy&& exec, ForwardIter first, Size n, Generator gen);

#include <iostream>
#include <algorithm>
#include <vector>

int main()
{
    std::vector<int> v(10);
    std::generate_n(std::begin(v), std::size(v), std::rand);
    for (auto it : v) {
        std::cout << it << std::endl;
    }
    return 0;
}

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