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

Loading Question ...

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.

Example:

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

// Inserts 1 to the collection. Returns true as the collection did not contain 1.
collection.insert(1);

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

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

// getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3.
collection.getRandom();

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

// getRandom should return 1 and 2 both equally likely.
collection.getRandom();


Seen this question in a real interview before?  
Yes
No
When did you encounter this question?  
last week
last month
last 3 month
last 6 month
more than 6 months
other
Which stage?  
Online Assessment
Phone Interview
Onsite Interview
Don't know
Which company?  
Adobe
Aetion
Airbnb
Alibaba
Amazon
Apple
Baidu
Bloomberg
Cloudera
Coursera
Cryptic Studios
Dropbox
eBay
Epic Systems
Expedia
Facebook
Fallible
Games
Gilt Groupe
GoDaddy
Goo
Google
Hedvig
Helix
Houzz
Hulu
Indeed
Intuit
IXL
LinkedIn
LiveRamp
Lyft
MAQ Software
Mathworks
Microsoft
NetEase
Netsuite
Palantir
Palantir Technologies
Pinterest
Pocket Gems
Poynt
Pure
Pure Storage
Rackspace
Riot
Riot Games
Samsung
Snapchat
Square
Storage
Tencent
TinyCo
Twitter
Two Sigma
Uber
Valve
WAP
Works Applications
Yahoo
Yahoo!
Yelp
Zappos
Zenefits