380. Insert Delete GetRandom O(1)

class RandomizedSet {
    HashSet<Integer> st;
    Random r;
    
    public RandomizedSet() {
        this.st = new HashSet<>();
        r = new Random();
    }
    
    public boolean insert(int val) {
        if(st.contains(val))  return false;
        st.add(val);
        return true;
    }
    
    public boolean remove(int val) {
        if(!st.contains(val)) return false;
        st.remove(val);
        return true;
    }

    public int getRandom() {
        Integer[] arr = st.toArray(new Integer[st.size()]);
        return arr[r.nextInt(st.size())];
    }
}

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