func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     long long n;     cin >> n;     vector<long long int> v(n);     for (long long int i = 0; i < n; i++) {       cin >> v[i];     }     sort((v).begin(), (v).end());     set<long long> s;     if (n == 1) {       cout << -1;     } else if (n == 2) {       s.insert(v[1] + (v[1] - v[0]));       s.insert(v[0] - (v[1] - v[0]));       if ((v[1] - v[0]) % 2 == 0) {         s.insert(v[0] + (v[1] - v[0]) / 2);       }       cout << s.size() <<   n ;       for (auto i : s) {         cout << i <<    ;       }     } else {       long long d = INT_MAX;       for (long long i = 0; i < n - 1; i++) {         d = min(d, v[i + 1] - v[i]);       }       bool missed = false;       bool noap = false;       for (long long i = 0; i < n - 1; i++) {         if (v[i + 1] == v[i] + d)           continue;         else {           if (v[i + 1] == v[i] + (d * 2)) {             if (missed == false) {               missed = true;               s.insert(v[i] + d);             } else {               noap = true;               break;             }           } else {             noap = true;             break;           }         }       }       if (noap) {         cout << 0;       } else if (missed) {         cout << 1 <<   n ;         cout << (*s.begin());       } else {         s.insert(v[0] - d);         s.insert(v[n - 1] + d);         cout << s.size() <<   n ;         for (auto i : s) {           cout << i <<    ;         }       }     }   }   