1.cpp

#include <algorithm>
#include <iostream>

using namespace std;

int remove(int *arr, int n) {
    int pos = 0;
    for (int i = 0 ; i != n ; ++i) {
        if (arr[i] == arr[pos])
            continue;
        arr[++pos] = arr[i];
    }
    return pos + 1;
}

int main() {
    int n;
    cin >> n;
    int *arr = new int[n];

    for (int i = 0 ; i != n ; ++i) {
        cin >> arr[i];
    }
    sort(arr, arr + n);

    int remain = remove(arr, n);

    // Output
    cout << remain << endl;
    for (int i = 0 ; i != remain ; i++)
        cout << arr[i] << " ";
    cout.flush();
    return 0;
}