你或许需要使用 stoll 而不是 stoi，例如

while (!v[s]) {
  v[s] = ans.size() + 1;
  ans.push_back(s);
  string Min = s, Max = s;
  sort (Min.begin(), Min.end());
  sort (Max.begin(), Max.end(), greater<char>());
  s = to_string(stoll(Max) - stoll(Min));
}