988D - Points and Powers of Two - CodeForces Solution

#include <bits/stdc++.h>
 
#define ll long long
#define el "\n"
#define endl "\n"
#define len(s) s.length()
#define io freopen("input.inp", "r", stdin);freopen("output.out", "w", stdout);
 
using namespace std;
 
int main()
{    
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    
    int n;
    cin >> n;

    int a[n+1];
    map<int, int> f;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
        f[a[i]] = 1;
    }

    for (int i = 1; i <= n; i++)
    {
        for (int mask = 0; mask <= 31; mask++)
            if (f.find(a[i]-(1<<mask)) != f.end() && f.find(a[i]+(1<<mask)) != f.end())
            {
                cout << 3 << el;
                cout << a[i]-(1<<mask) << ' ' << a[i] << ' ' << a[i]+(1<<mask);
                return 0;
            }
    }

    for (int i = 1; i <= n; i++)
        for (int mask = 0; mask <= 31; mask++)
        {
            if (f.find(a[i]+(1<<mask)) != f.end())
            {
                cout << 2 << el;
                cout << a[i] << ' ' << a[i]+(1<<mask);
                return 0;
            }
        }

    cout << 1 << el;
    cout << a[1];
    return 0;
}