func_code_string: #include <bits/stdc++.h>   using namespace std;   int N;   bool valid(int P, int d, vector<int> guess) {     if (P >= N) {       return true;     }     if (P == 0) {       if (valid(P + 1, d, guess)) return true;       guess[P] -= d;       if (valid(P + 1, d, guess)) return true;       guess[P] += d;       guess[P] += d;       if (valid(P + 1, d, guess)) return true;       guess[P] -= d;     } else {       if (guess[P] == guess[P - 1]) {         if (valid(P + 1, d, guess)) return true;       } else if ((guess[P] - d) == guess[P - 1]) {         guess[P] -= d;         if (valid(P + 1, d, guess)) return true;         guess[P] += d;       } else if ((guess[P] + d) == guess[P - 1]) {         guess[P] += d;         if (valid(P + 1, d, guess)) return true;         guess[P] -= d;       }     }     return false;   }   int main() {     cin >> N;     vector<int> V(N);     for (int i = 0; i < N; i++) cin >> V[i];     for (int d = 0; d <= 100; d++) {       if (valid(0, d, V)) {         cout << d <<   n ;         return 0;       }     }     cout << -1 <<   n ;     return 0;   }   