Language: C++

int main(){
    string S, T;
    cin >> S >> T;
    
    if(T.length() > S.length()){
        cout << "UNRESTORABLE" << endl;
    }
    
    int L = T.length();
    
    string ans = "";
    for(int i = 0; i < 50; ++i){
        ans += 'z';
    }
    string unti = ans;
    
    for(int i = S.length() - L; i >= 0; --i){
        bool flag = true;
        for(int j = 0; j < L; ++j){
//            cout << S[i + j] << " ";
            if(S[i + j] == '?'){
                continue;
            } else if(S[i + j] == T[j]){
                continue;
            } else {
                flag = false;
                break;
            }
        }
        string tmp = "";
        if(flag){
            for(int j = 0; j < S.length(); ++j){
                if(j < i || (j > i + L)){
                    if(S[j] == '?'){
                        tmp += 'a';
                    } else {
                        tmp += S[j];
                    }
                } else {
                    tmp += T[j - i];
                }
            }
            ans = min(ans, tmp);
        }
    }
    if(ans < unti){
        cout << ans << endl;
        return 0;
    }
    cout << "UNRESTORABLE" << endl;
}



Compiler output:
a.cc: In function 'int main()':
a.cc:2:5: error: 'string' was not declared in this scope
    2 |     string S, T;
      |     ^~~~~~
a.cc:3:5: error: 'cin' was not declared in this scope
    3 |     cin >> S >> T;
      |     ^~~
a.cc:3:12: error: 'S' was not declared in this scope
    3 |     cin >> S >> T;
      |            ^
a.cc:3:17: error: 'T' was not declared in this scope
    3 |     cin >> S >> T;
      |                 ^
a.cc:6:9: error: 'cout' was not declared in this scope
    6 |         cout << "UNRESTORABLE" << endl;
      |         ^~~~
a.cc:6:35: error: 'endl' was not declared in this scope
    6 |         cout << "UNRESTORABLE" << endl;
      |                                   ^~~~
a.cc:11:11: error: expected ';' before 'ans'
   11 |     string ans = "";
      |           ^~~~
      |           ;
a.cc:13:9: error: 'ans' was not declared in this scope
   13 |         ans += 'z';
      |         ^~~
a.cc:15:11: error: expected ';' before 'unti'
   15 |     string unti = ans;
      |           ^~~~~
      |           ;
a.cc:30:15: error: expected ';' before 'tmp'
   30 |         string tmp = "";
      |               ^~~~
      |               ;
a.cc:35:25: error: 'tmp' was not declared in this scope
   35 |                         tmp += 'a';
      |                         ^~~
a.cc:37:25: error: 'tmp' was not declared in this scope
   37 |                         tmp += S[j];
      |                         ^~~
a.cc:40:21: error: 'tmp' was not declared in this scope
   40 |                     tmp += T[j - i];
      |                     ^~~
a.cc:43:13: error: 'ans' was not declared in this scope
   43 |             ans = min(ans, tmp);
      |             ^~~
a.cc:43:28: error: 'tmp' was not declared in this scope
   43 |             ans = min(ans, tmp);
      |                            ^~~
a.cc:43:19: error: 'min' was not declared in this scope; did you mean 'main'?
   43 |             ans = min(ans, tmp);
      |                   ^~~
      |                   main
a.cc:46:8: error: 'ans' was not declared in this scope
   46 |     if(ans < unti){
      |        ^~~
a.cc:46:14: error: 'unti' was not declared in this scope
   46 |     if(ans < unti){
      |              ^~~~
a.cc:47:9: error: 'cout' was not declared in this scope
   47 |         cout << ans << endl;
      |         ^~~~
a.cc:47:24: error: 'endl' was not declared in this scope
   47 |         cout << ans << endl;
      |                        ^~~~
a.cc:50:5: error: 'cout' was not declared in this scope
   50 |     cout << "UNRESTORABLE" << endl;
      |     ^~~~
a.cc:50:31: error: 'endl' was not declared in this scope
   50 |     cout << "UNRESTORABLE" << endl;
      |                               ^~~~