func_code_string: #include <bits/stdc++.h>   using namespace std;   inline void optimizeIO() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);   }   const int nmax = 150005;   const long long LINF = 1e17;   int ara[110];   set<int> SET;   int main() {     optimizeIO();     int n;     cin >> n;     for (int i = 1; i <= n; i++) {       cin >> ara[i];       SET.insert(ara[i]);     }     int siz = SET.size();     if (siz > 3) {       cout << -1;       return 0;     }     if (siz == 3) {       vector<int> v;       for (auto x : SET) v.push_back(x);       int a = v[2] - v[1];       int b = v[1] - v[0];       if (a != b) {         cout << -1;         return 0;       }       if (a == b) {         cout << a << endl;         return 0;       }     }     if (siz == 2) {       vector<int> v;       for (auto x : SET) v.push_back(x);       int a = v[1] - v[0];       if (a % 2 == 1) {         cout << a << endl;         return 0;       }       if (a % 2 == 0) {         cout << a / 2 << endl;         return 0;       }     }     if (siz == 1) {       cout << 0 << endl;     }     return 0;   }   