#randomization

11 randomization interview questions, asked at Google, Apple, Meta and 6 more companies. Last asked Sep 2026.

Insert, delete and get random in O(1) with duplicatesCodingDesign a collection of integers that allows duplicates and supports, each in average O(1) time: 1. insert(val): add one copy of val; return whether val was absent before. 2…
Last asked Sep 2026
Weighted random pick with add and removeCoding1. Given positive weights, return a random index with probability proportional to its weight. 2. Turn it into a structure of weighted keys that supports adding a key, removing a…
Last asked Jul 2026
+1
Random pick weighted by populationCodingGiven countries and their populations, write a picker that returns a random country with probability proportional to its population. Build prefix sums once, draw a random number…
Last asked Jul 2026
+2
Insert, delete and get random in O(1)CodingDesign a set with insert(val), remove(val) and getrandom(), each in average O(1) time. getrandom returns each current element with equal probability.
Last asked May 2026
Substring search and weighted random samplingCodingTwo problems for a machine learning engineer screen: 1. Find where a pattern occurs in a text, and discuss doing better than checking every position. 2. Pick an item at random…
Last asked Mar 2026
Deck of cards with shuffle, draw and sortOO designModel a deck of playing cards with classes for cards and the deck. Implement a fair shuffle (every order equally likely, Fisher-Yates), drawing cards, and putting the deck back in…
Last asked Mar 2026
Playlist with add, remove and shuffleCodingImplement a video playlist that supports adding a title, removing a title and shuffling the order, along with playing the next title. Aim for constant-time add and remove, a fair…
Last asked Jan 2026
Weighted random value generatorCodingGiven values with positive weights, write a generator that returns a value at random with probability proportional to its weight. Build it once and answer many calls quickly, and…
Last asked Jan 2026
Set with constant-time insert, delete and get randomCodingDesign a set with add, remove and getrandom, all in average O(1); getrandom returns each element with equal probability. Handle empty-set and missing-element cases. Follow-up: how…
Last asked Jan 2026
Shuffle an array with a random-integer functionCodingUsing only a function that returns a uniform random integer in a range, shuffle an array (for example a deck of cards) so every permutation is equally likely. Implement…
Last asked Dec 2025
Random point in non-overlapping squaresCodingDefine a class for a square on the plane and return a uniformly random point inside it. Follow-up: given many non-overlapping squares, return a point that is uniformly random over…
Last asked Jul 2025