380.cpp

class RandomizedSet {
  vector<int> nums;
  unordered_map<int, int> m;

public:
  /** Initialize your data structure here. */
  RandomizedSet() {}

  /** Inserts a value to the set. Returns true if the set did not already
   * contain the specified element. */
  bool insert(int val) {
    if (m.find(val) != m.end())
      return false;
    nums.emplace_back(val);
    m[val] = nums.size() - 1;
    return true;
  }

  /** Removes a value from the set. Returns true if the set contained the
   * specified element. */
  bool remove(int val) {
    if (auto it = m.find(val); it == m.end())
      return false;
    else {
      m[nums.back()] = it->second;
      nums[it->second] = nums.back();
      nums.pop_back();
      m.erase(it);
      return true;
    }
  }

  /** Get a random element from the set. */
  int getRandom() { return nums[rand() % nums.size()]; }
};

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * RandomizedSet* obj = new RandomizedSet();
 * bool param_1 = obj->insert(val);
 * bool param_2 = obj->remove(val);
 * int param_3 = obj->getRandom();
 */