Insert Delete GetRandom O(1).cpp

class RandomizedSet {
public:
set<int>st;
int i=-1;
    RandomizedSet() {
        
    }
    
    bool insert(int val) {
        if(st.find(val)==st.end())
        {
            st.insert(val);
            return true;
        }
        return false;
    }
    
    bool remove(int val) {
        if(st.find(val)==st.end())
        {
            return false;
        }
        st.erase(val);
        return true;
    }
    
    int getRandom() {
        int idx = rand()%st.size();
        auto it = st.begin();
        for (int i = 0; i < idx; i++)
        {
            it++;
        }
        return *it;

    }
};

/**
 * 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();
 */