message: Update insert-delete-getrandom-o1.cpp
diff: class RandomizedSet {
  public:
  /** Initialize your data structure here. */
  - RandomizedSet() {
  + RandomizedSet() : gen_(random_device()()) {
  }
  @@ -37,12 +37,14 @@ public:
  /** Get a random element from the set. */
  int getRandom() {
  - return set_[rand() % set_.size()];
  + uniform_int_distribution<int> dist(0, set_.size() - 1);
  + return set_[dist(gen_)];
  }
  private:
  vector<int> set_;
  unordered_map<int, int> used_;
  + default_random_engine gen_;
  };
  /**
  