381B - Sereja and Stairs - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
#define fst ios_base::sync_with_stdio(false);cin.tie(NULL);
#define ll long long 
#define sz(x) int(x.size())
#define ft first
#define sd second
#define endl '\n'
#define pb push_back
#define yes cout<<"YES"<<endl
#define no cout<<"NO"<<endl
void solve()
{  
    int v[12312];
    int n; cin >> n;    
    for(int i = 0; i < n; i++){
        int x; cin >> x;
        v[x]++;
    }
 
    vector<int> res;
    int maxi = 0;
    for(int i = 1; i <= 5000; i++)
        if(v[i] >= 1){
            maxi = i;
            v[i]--;
            res.push_back(i);
        }
    for(int i = maxi-1; i >= 1; i--)
        if(v[i] >= 1){
            v[i]--;
            res.push_back(i);
        }
    cout << res.size() << endl;
    for(int val : res)
        cout << val << " ";
    cout << endl;
}
int32_t main()
{
    fst
    int ttt=1;
    //cin >> ttt;
    while(ttt--)
    {
        solve();
    }
    return 0;
}