Leetcode 380. Insert Delete GetRandom O(1)

380. Insert Delete GetRandom O(1)

アプローチ

ArrayList, HashSet

class RandomizedSet {

  public ArrayList<Integer> arrayList;
    public Set<Integer> set;
    public Random rm;
    public RandomizedSet() {
        arrayList = new ArrayList<>();
        set = new HashSet<>();
        rm = new Random();
    }

    public boolean insert(int val) {
        if(set.contains(val)){
            return false;
        }
        arrayList.add(val);
        set.add(val);
        return true;
    }

    public boolean remove(int val) {
        if(!set.contains(val)){
            return false;
        }

        set.remove(val);
        arrayList.remove(new Integer(val));
        return true;
    }

    public int getRandom() {
        int idx = rm.nextInt(set.size());
        return arrayList.get(idx);
    }
}