Package g0301_0400.s0381_insert_delete_getrandom_o1_duplicates_allowed

Class RandomizedCollection

java.lang.Object
g0301_0400.s0381_insert_delete_getrandom_o1_duplicates_allowed.RandomizedCollection
public class RandomizedCollection extends java.lang.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.

  • Constructor Summary

    Constructors
    Constructor
    Description
    RandomizedCollection()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    getRandom()
     
    boolean
    insert(int val)
     
    boolean
    remove(int val)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • RandomizedCollection

      public RandomizedCollection()

  • Method Details

    • insert

      public boolean insert(int val)

    • remove

      public boolean remove(int val)

    • getRandom

      public int getRandom()