题解

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e4+10;
int a[maxn];
int b[maxn], n, sum;
int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int y;
        cin >> y;
        a[y]++;
        b[i] = y;
    }
    sort(b, b + n + 1);
    for (int i = 1; i <= b[n]; i++) {
        if (a[i] != 0)
            sum++;
    }
    cout << sum << endl;
    for (int i = 1; i <= b[n]; i++) {
        if (a[i] != 0)
            cout << i << " ";
    }
    return 0;
}