【来自ChatGPT】

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

int main() {
    int n;
    std::cin >> n;

    std::vector<int> numbers(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> numbers[i];
    }

    std::set<int> unique_numbers(numbers.begin(), numbers.end());

    std::vector<int> sorted_unique(unique_numbers.begin(), unique_numbers.end());
    std::sort(sorted_unique.begin(), sorted_unique.end());

    std::cout << sorted_unique.size() << std::endl;
    for (int num : sorted_unique) {
        std::cout << num << " ";
    }
    std::cout << std::endl;

    return 0;
}