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.