Interview questions

Double Cipher Decryption

Decrypt a message that has been encrypted twice using two different letter substitution mappings applied in sequence. You must reverse both encryption layers to recover…

Companies: Upstart

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

Find duplicated files

Find duplicated files in a given directory. How to optimize? What if files changes? How to find duplicated files among many machines?

Companies: Anthropic, Snowflake

Last reported Oct 2026

Find Most Called Function in Stack Trace

Given a list representing a stack trace with functions and directional arrows ('->' for calls, '<-' for returns), determine which function is called the most…

Companies: Roblox

Last reported Oct 2026

Image Transformation Pipeline

Given a prebuilt environment, implement Python functions that apply a series of transformations to a set of images and write the results to an output…

Companies: Anthropic

Last reported Oct 2026

Implement a REST Endpoint That Aggregates Data from Multiple Internal Services

Design and implement a GET /api/bootstrap REST endpoint that accepts a user_id and aggregates data from multiple internal services (Consumer, Address, Payments) into a single…

Companies: DoorDash

Last reported Oct 2026

Implement a Tail Utility

Implement a program that displays the last N lines of a given file. Pay attention to your buffering strategy and how you handle reading the…

Companies: Confluent

Last reported Oct 2026

Implement Kac Ring Simulation with O(1) Step Query

Implement a Kac Ring data structure consisting of a circular ring of N positions, each with a color (0 or 1, or equivalently White/Black) and…

Companies: The Voleon Group, Voleon

Last reported Oct 2026

IPv4 Address Iterator

Implement an iterator that traverses IPv4 addresses starting from a given address, supporting forward iteration, reverse iteration, and CIDR block iteration.

Companies: Anthropic, OpenAI

Data Structure Design · Networking

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

Max Stack

Design a stack data structure that supports standard push, pop, and top operations, along with a getMax operation that retrieves (but does not remove) the…

Companies: Confluent, Everpure, LinkedIn, Walmart Labs

Design · Doubly-Linked List · Linked List · Ordered Set

Last reported Oct 2026

Maximum Bitwise AND After Increment Operations

Given an integer array nums and two integers k and m, perform at most k increment operations on any elements, then return the maximum possible…

Companies: Amazon

Array · Bit Manipulation · Greedy · Sorting

Last reported Oct 2026

Maximum Coins From K Consecutive Bags

Given non-overlapping segments where every integer position in [li, ri] holds ci coins, find the maximum total coins covered by any contiguous window of k…

Companies: Amazon

Array · Binary Search · Greedy · Prefix Sum

Last reported Oct 2026

Populating Next Right Pointers in Each Node II

Populate each node's next pointer to point to its immediate right neighbor on the same level (or NULL if none) in a binary tree that…

Companies: Crusoe, Meta

Last reported Oct 2026

Put Boxes Into the Warehouse I

Given arrays of box heights and warehouse room heights, maximize how many boxes can be placed knowing a box can only reach a room if…

Companies: Pinterest

Array · Greedy · Sorting

Last reported Oct 2026

Put Boxes Into the Warehouse II

Given box sizes and a sequence of warehouse slot heights, maximize how many boxes can be placed into the slots under the constraint that a…

Companies: Pinterest

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

Sliding Window Median

Given an array and window size k, return the median of each sliding window as it moves right by one. The core challenge is maintaining…

Companies: Meta, Microsoft, Spotify

Last reported Oct 2026

Sliding Window Rate Limiter

Implement a rate limiter using a sliding window algorithm that tracks and limits the number of requests allowed within a given time window. Extend the…

Companies: Adobe, Amazon, Cloudflare, CrowdStrike +4

Last reported Oct 2026

Split BST

Given a BST and a value V, partition the tree into two BSTs where one contains all nodes with values ≤ V and the other…

Companies: Meta

Last reported Oct 2026

Subarray Product Less Than K

Count the number of contiguous subarrays of positive integers whose product is strictly less than k. Because all nums > 0, this is a sliding-window/two-pointer…

Companies: Apple

Array · Binary Search · Prefix Sum · Sliding Window

Last reported Oct 2026