Insert Delete GetRandom O(1)

O(1)의 속도로 저장, 삭제 및 랜덤한 데이터를 가져올 수 있는 set을 만드는 문제

class RandomizedSet {
public:
    unordered_map<int, int> _table{};
    vector<int> _items{};

    RandomizedSet() {
        srand(time(nullptr)); 
    }
    
    bool insert(int val) {
        if (0 < _table.count(val))
        {
            return false;
        }

        _table.insert({val, _items.size()});
        _items.push_back(val);

        return true;
    }
    
    bool remove(int val) {
        if (0 < _table.count(val))
        {
            int index = _table[val];
            _items[index] = _items.back();
            _items.pop_back();
            _table[_items[index]] = index;

            _table.erase(val);

            return true;
        }

        return false;
    }
    
    int getRandom() {
        
        int randomIndex = rand() % _items.size();

        return _items[randomIndex];
    }
};

/**
 * 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();
 */