#data structures

16 data structures interview questions, asked at Amazon, Apple, Google and 6 more companies. Last asked Sep 2026.

Is a number line fully covered after each landing point?CodingPoints land one at a time on the segment 0, 50. Each point covers the interval of length 1 centred on it (0.5 to each side), and covered parts stay covered. After each landing…
Last asked Sep 2026
Return every word that starts with a prefixCodingBuild a structure over a word list, once, that answers many prefix queries: for a prefix, return every word in the list that starts with it, without rescanning the whole list. A…
Last asked Sep 2026
Design a dictionary whose keys and values have mixed typesCodingDesign a key-value dictionary in which keys and values can be of different types and lengths. Explain how you hash and compare keys of different types, how collisions are handled…
Last asked Aug 2026
Bookshelf with book CRUD and a stable bookmarkCodingDesign a bookshelf that supports adding, reading, updating and removing books, plus a bookmark that keeps pointing at the right book while books are added or removed around it.
Last asked Aug 2026
Min-priority queue without a library heapCodingImplement a min-priority queue yourself, without a library heap: insert, look at the minimum, and remove the minimum. Give the cost of each operation.
Last asked Aug 2026
Reusable locker allocation systemCodingBuild a system that hands out lockers and takes them back so they can be used again: assign a free locker on request, release it later, and keep both operations fast as the number…
Last asked Aug 2026
Thread safety and deadlocks, explained and demonstratedCodingA fast concepts round. What makes code thread-safe? Show the common ways a deadlock happens (for example two threads taking two locks in opposite order) and the ways to prevent…
Last asked Aug 2026
Deep equality of two recordsCodingWrite a function that decides whether two records are deeply equal: the same keys, with values that are equal all the way down through nested maps and lists. Agree with the…
Last asked Jun 2026
Last-click attributionCodingImplement APIs that record users' ad clicks and, when a user converts, credit the conversion to that user's most recent click. Settle the open questions first, such as an…
Last asked May 2026
Cache with a snapshot printerCodingBuild a cache much like an LRU cache, with one extra function, snapshot(cache), that prints the cache's current contents in order. A second part builds on it with a compressed…
Last asked Feb 2026
Data structure fundamentals: arrays, linked lists, hash tables and treesCodingAnswer quick fundamentals questions: the time complexity of common sorting algorithms; arrays versus linked lists, including the cost of inserting at the head and in the middle…
Last asked Feb 2026
Design a hash map without built-in librariesCodingImplement a hash map with put, get and remove without using any built-in hash table. Choose the bucket layout, the hash function and how collisions are handled, and explain when…
Last asked Nov 2025
LFU cache, then distribute itCodingDesign and implement a least-frequently-used cache with get and put in O(1), evicting the least used key and, among ties, the least recently used. The input then becomes a stream…
Last asked Nov 2025
Resize a hash map without long pausesCodingExplain how a hash map works and how it grows its bucket array. Resizing all at once can stall a request for a long time on a big map. How would you avoid that? Discuss…
Last asked Oct 2025
Design a string type: memory layout, moves and thread safetyCodingWhat is a string in a programming language? Describe what fields a string struct holds (for example in Rust: pointer, length, capacity) and how you would implement one yourself…
Last asked Jul 2025
Python lists, dicts and concurrencyCodingAnswer Python fundamentals questions: how lists and dicts work underneath and the cost of their operations, then multithreading versus multiprocessing, the GIL, and when to use…
Last asked Jul 2025