381. Insert Delete GetRandom O(1) - Duplicates allowed

Design a data structure that supports all following operations in average O(1) time.

Note: Duplicate elements are allowed.

  1. insert(val): Inserts an item val to the collection.
  2. remove(val): Removes an item val from the collection if present.
  3. getRandom: Returns a random element from current collection of elements. The probability of each element being returned is linearly related to the number of same value the collection contains.


// Init an empty collection.
RandomizedCollection collection = new RandomizedCollection();

// Inserts 1 to the collection. Returns true as the collection did not contain 1.

// Inserts another 1 to the collection. Returns false as the collection contained 1. Collection now contains [1,1].

// Inserts 2 to the collection, returns true. Collection now contains [1,1,2].

// getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3.

// Removes 1 from the collection, returns true. Collection now contains [1,2].

// getRandom should return 1 and 2 both equally likely.