#include <algorithm>
#include <array>
#include <iostream>
#include <numeric>
#include <random>
#include <vector>
 
constexpr std::size_t seq_len = 16;
constexpr std::size_t num_balls = 52;
 
int main()      // this is not generalized for an odd sequence length
{
    auto generator = std::mt19937{ std::random_device{}() };
 
    auto balls = std::array<int, num_balls>{};
    std::iota(balls.begin(), balls.end(), 1);
    std::shuffle(balls.begin(), balls.end(), generator);
 
    auto sequence = std::vector<int>{ balls.begin(), balls.begin() + seq_len / 2 };
 
    std::shuffle(balls.begin(), balls.begin() + seq_len/2, generator);
    sequence.insert(sequence.end(), balls.begin(), balls.begin() + seq_len/2);
 
    for (auto ball : sequence)
        std::cout << ball << ' ';
}

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