LeetCode 380: Insert Delete GetRandom O(1)

class RandomizedSet {
    
    Map<Integer, Integer> indexMap;
    List<Integer> indexes;
    
    /** Initialize your data structure here. */
    public RandomizedSet() {
        indexes = new ArrayList<>();
        indexMap = 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 (indexMap.containsKey(val)) {
            return false;
        }
        indexMap.put(val, indexes.size());
        indexes.add(val);
        return true;
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    public boolean remove(int val) {
        if (!indexMap.containsKey(val)) {
            return false;
        }
         
        int index = indexMap.get(val);
        if (index < indexes.size() - 1) {
            indexMap.put(indexes.get(indexes.size() - 1), index);
            indexes.set(index, indexes.get(indexes.size() - 1));
        }
        indexMap.remove(val);
        indexes.remove(indexes.size() - 1);
        return true;
    }
    
    /** Get a random element from the set. */
    public int getRandom() {
        return indexes.get(new Random().nextInt(indexes.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();
 */

Follow up questions, what if dup allows:

1. Map<Value, Queue<Indexes>> if it looks like a queue first in first out.

2. Map<Value, Map<Index, Indexes>> User can remove the nth value.