Design a data structure that supports all following operations inaverageO(1)time.

1. insert(val): Inserts an item val to the set if not already present.
2. remove(val): Removes an item val from the set if present.
3. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.

class RandomizedSet {
    private HashMap<Integer, Integer> map;
    private ArrayList<Integer> list;

    /** Initialize your data structure here. */
    public RandomizedSet() {
        list = new ArrayList<>();
        map = new HashMap<>();
    }

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    public boolean insert(int val) {
        if(map.containsKey(val))
            return false;
        list.add(val);
        map.put(val, list.size() - 1);
        return true;
    }

    /** Removes a value from the set. Returns true if the set contained the specified element. */
    public boolean remove(int val) {
        if(!map.containsKey(val))
            return false;

        int index = map.get(val);
        list.set(index, list.get(list.size() - 1));
        map.put(list.get(list.size() - 1), index);
        map.remove(val);
        list.remove(list.size() - 1);

        return true;
    }

    /** Get a random element from the set. */
    public int getRandom() {
        Random rand = new Random();
        return list.get(rand.nextInt(list.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();
 */