380. Insert Delete GetRandom O(1) — 12th June LeetCode Challenge

Design a data structure that supports all following operations in average O(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.

Example:

// Init an empty set.
RandomizedSet randomSet = new RandomizedSet();
// Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomSet.insert(1);
// Returns false as 2 does not exist in the set.
randomSet.remove(2);
// Inserts 2 to the set, returns true. Set now contains [1,2].
randomSet.insert(2);
// getRandom should return either 1 or 2 randomly.
randomSet.getRandom();
// Removes 1 from the set, returns true. Set now contains [2].
randomSet.remove(1);
// 2 was already in the set, so return false.
randomSet.insert(2);
// Since 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();

Here is my solution:

class RandomizedSet {
    Map<Integer, Integer> valueMap;
    List<Integer> valueList;
/** Initialize your data structure here. */
    public RandomizedSet() {
        valueMap = new HashMap<>();
        valueList = new ArrayList<>();
    }
    
    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    public boolean insert(int val) {
        if (valueMap.containsKey(val)) {
            return false;
        }
        valueMap.put(val, valueList.size());
        valueList.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 (!valueMap.containsKey(val)) {
            return false;
        }
        int index = valueMap.get(val);
        int lastIndex = valueList.size() - 1;
        int lastElement = valueList.get(lastIndex);
        
        Collections.swap(valueList, index, lastIndex);
        valueList.remove(lastIndex);
        
        valueMap.put(lastElement, index);
        valueMap.remove(val);
        return true;
    }
    
    /** Get a random element from the set. */
    public int getRandom() {
        int randomIndex = new Random().nextInt(valueList.size());
        return valueList.get(randomIndex);        
    }
}
/**
 * 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();
 */

You can checkout full explanation by watching below video