380. Insert Delete GetRandom O(1)

class RandomizedSet {
private:
    unordered_map<int, int> m;
    vector<int> nums;
public:
    RandomizedSet() {}

    bool insert(int val)
    {
        if(m.count(val)) return false;

        nums.push_back(val);

        m[val] = nums.size() - 1;

        return true;
    }

    bool remove(int val)
    {
        if (!m.count(val)) return false;

        int lastElement = nums.back();

        nums[m[val]] = lastElement;
        m[lastElement] = m[val];

        nums.pop_back();
        m.erase(val);
        return true;
    }

    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();
 */

• T: $O(1)$
• S: $O(N)$