public class RandomizedCollection
extends Object
381 - Insert Delete GetRandom O(1) - Duplicates allowed\.
Hard
`RandomizedCollection` is a data structure that contains a collection of numbers, possibly duplicates (i.e., a multiset). It should support inserting and removing specific elements and also removing a random element.
Implement the `RandomizedCollection` class:
* `RandomizedCollection()` Initializes the empty `RandomizedCollection` object.
* `bool insert(int val)` Inserts an item `val` into the multiset, even if the item is already present. Returns `true` if the item is not present, `false` otherwise.
* `bool remove(int val)` Removes an item `val` from the multiset if present. Returns `true` if the item is present, `false` otherwise. Note that if `val` has multiple occurrences in the multiset, we only remove one of them.
* `int getRandom()` Returns a random element from the current multiset of elements. The probability of each element being returned is **linearly related** to the number of same values the multiset contains.
You must implement the functions of the class such that each function works on **average** `O(1)` time complexity.
**Note:** The test cases are generated such that `getRandom` will only be called if there is **at least one** item in the `RandomizedCollection`.
**Example 1:**
**Input**
["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"]
[ [], [1], [1], [2], [], [1], []]
**Output:** [null, true, false, true, 2, true, 1]
**Explanation:**
RandomizedCollection randomizedCollection = new RandomizedCollection();
randomizedCollection.insert(1); // return true since the collection does not contain 1.
// Inserts 1 into the collection.
randomizedCollection.insert(1); // return false since the collection contains 1.
// Inserts another 1 into the collection. Collection now contains [1,1].
randomizedCollection.insert(2); // return true since the collection does not contain 2.
// Inserts 2 into the collection. Collection now contains [1,1,2].
randomizedCollection.getRandom(); // getRandom should:
// - return 1 with probability 2/3, or
// - return 2 with probability 1/3.
randomizedCollection.remove(1); // return true since the collection contains 1.
// Removes 1 from the collection. Collection now contains [1,2].
randomizedCollection.getRandom(); // getRandom should return 1 or 2, both equally likely.
**Constraints:**
* -231 <= val <= 231 - 1
* At most 2 * 105 calls **in total** will be made to `insert`, `remove`, and `getRandom`.
* There will be **at least one** element in the data structure when `getRandom` is called.