380. Insert Delete GetRandom O(1)

class RandomizedSet {
public:
    vector<int> data;
    unordered_map<int,int> m;   // <val,index in data vector>
    /** 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.count(val))   return false;
        m[val] = data.size();
        data.push_back(val);
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    bool remove(int val) {
        if (!m.count(val))   return false;
        int idx = m[val];
        m[data.back()] = idx;
        data[idx] = data.back();
        m.erase(val);
        data.pop_back();
        return true;
    }
    
    /** Get a random element from the set. */
    int getRandom() {
        return data[rand() % data.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();
 */