Interview questions

All O`one Data Structure

Design a data structure that supports incrementing and decrementing string counts (removing keys when their count drops to zero) and can return any key with…

Companies: Atlassian, LinkedIn, Meta, Microsoft +2

Design · Doubly-Linked List · Hash Table · Linked List

Last reported Oct 2026

Group Anagrams

Group the input strings into lists of anagrams — i.e., strings that contain the same multiset of letters — and return the groups in any…

Companies: Amazon, Apple, Arize Ai, Bloomberg +14

Array · Hash Table · Sorting · String

Last reported Oct 2026

Top K Frequent Words

Count word frequencies and return the k most frequent words sorted by descending frequency, breaking ties by lexicographical order. The core challenge is combining frequency…

Companies: Apple, Microsoft, Oracle, Robinhood

Array · Bucket Sort · Counting · Hash Table

Last reported Oct 2026

Find Duplicate File in System

Parse each directory string to extract full file paths and their contents, then group paths by identical file content and return all groups containing at…

Companies: Anthropic, Google, OpenAI

Array · Hash Table · String

Last reported Oct 2026

Longest Substring Without Repeating Characters

Find the length of the longest contiguous substring that contains no repeated characters. This is a classic sliding-window / two-pointer problem where you track seen…

Companies: Amazon, Apple, Autodesk, Bloomberg +12

Hash Table · Sliding Window · String

Last reported Oct 2026

Lowest Common Ancestor of a Binary Tree III

Companies: Amazon, Apple, Meta

Binary Lifting · Binary Tree · Hash Table · Lowest Common Ancestor

Last reported Oct 2026

Shortest Word Distance II

Given a list of words, design a class that can answer repeated queries returning the minimum index distance between two given words; optimize for many…

Companies: LinkedIn

Array · Design · Hash Table · String

Last reported Oct 2026

Top K Frequent Elements

Given an integer array and k, return the k most frequent elements — the core challenge is to count element frequencies and extract the top-k…

Companies: Amazon, Bloomberg, Google, Meta +9

Array · Bucket Sort · Counting · Divide and Conquer

Last reported Oct 2026

Insert Delete GetRandom O(1)

Design a data structure supporting insert(val), remove(val), and getRandom() — which returns a uniformly random existing element — with each operation in average O(1) time…

Companies: Amazon, Apple, Bloomberg, Citadel +7

Array · Design · Hash Table · Math

Last reported Sep 2026

Logger Rate Limiter

Implement a logger that decides whether to print a message at a given timestamp: return true if the message hasn't been printed in the last…

Companies: Amazon, Bloomberg, Google, Microsoft +3

Data Stream · Design · Hash Table

Last reported Sep 2026

Word Break

Determine whether the string s can be segmented into a sequence of one or more words from wordDict (words may be reused). The core challenge…

Companies: Amazon, Google, Grammarly, Meta +3

Array · Brute-Force Search · Dynamic Programming · Hash Table

Last reported Sep 2026

First Unique Character in a String

Return the index of the first character in s that occurs exactly once (or -1 if none). This is typically solved by counting character frequencies…

Companies: Apple, Goldman Sachs

Counting · Hash Table · Queue · String

Last reported Sep 2026

Bus Routes

Given repeating bus routes and start/target stops, find the minimum number of bus rides required to go from source to target (or -1 if impossible)…

Companies: Amazon, Bloomberg, Coupang, PayPal +3

Array · Breadth-First Search · Hash Table

Last reported Sep 2026

Shortest Uncommon Substring in an Array

For each string in an array, find the shortest substring that does not occur in any other string (choose the lexicographically smallest one among ties)…

Companies: Airbnb

Array · Hash Table · String · Trie

Last reported Sep 2026

Minimum Window Substring

Find the smallest substring of s that contains all characters of t (including duplicates), or return "" if none exists. This is typically solved with…

Companies: Amazon, LinkedIn, Lyft, Meta +2

Hash Table · Sliding Window · String

Last reported Sep 2026

Insert Delete GetRandom O(1) - Duplicates allowed

Design a data structure for a multiset that supports insert(val) (adding even duplicate occurrences), remove(val) (removing a single occurrence), and getRandom() (returning an…

Companies: CrowdStrike, LinkedIn, Okta

Array · Design · Hash Table · Math

Last reported Sep 2026

Task Scheduler

Given tasks labeled A–Z and a cooldown n, compute the minimum number of CPU intervals (including idles) to finish all tasks so that identical tasks…

Companies: Amazon, Apple, Databricks, Docker +3

Array · Counting · Greedy · Hash Table

Last reported Sep 2026

Design Excel Sum Formula

Design a spreadsheet supporting set/get and sum operations where sum formulas can reference individual cells and rectangular ranges; the core challenge is maintaining a…

Companies: Airbnb, Discord

Array · Design · Graph Theory · Hash Table

Last reported Sep 2026

Design HashMap

Implement a HashMap for integer keys/values without using built-in hash table libraries that supports put, get, and remove operations. The core challenge is to design…

Companies: Anduril, Canva, Chewy, Goldman Sachs +2

Array · Design · Hash Function · Hash Table

Last reported Sep 2026

Design Spreadsheet

Design a Spreadsheet class with 26 columns and a specified number of rows that supports setCell and resetCell operations and stores integer values (unset cells…

Companies: Citadel, Discord

Array · Design · Hash Table · Matrix

Last reported Sep 2026

Fraction to Recurring Decimal

Convert a fraction to its decimal string form, enclosing any repeating fractional cycle in parentheses. The core challenge is simulating long division while handling sign…

Companies: Goldman Sachs, Meta

Hash Table · Math · String

Last reported Sep 2026

Number of Islands II

Given an initially all-water m×n grid, process a sequence of add-land operations and return the number of islands (4-directionally connected land components) after each…

Companies: LinkedIn, Microsoft, Uber

Array · Hash Table · Union-Find

Last reported Sep 2026