Coding & Algorithms Interview Questions
Practice 2,960 real Coding & Algorithms interview questions for 2026. Coding & Algorithms interview questions for top tech firms like Meta, Amazon, Google, Uber, and TikTok — real questions from actual interviews with detailed solutions — to power your interview preparation. This collection is sharply focused on algorithmic patterns (arrays, strings, sliding windows, trees/graphs, dynamic programming, greedy, two-pointers, and hashing), clean, review-ready code, and the explanation skills that distinguish hires. In 2026 expect familiar medium-to-hard problems plus newer twists: AI-enabled or multi-file coding rounds at some companies, more emphasis on explainability and edge-case reasoning, and occasional real-world performance constraints (streaming, concurrency, memory limits). Interviewers evaluate problem framing, algorithm choice, complexity trade-offs, test-case thinking, and communication under time pressure. Best prep mixes pattern-based practice, timed mock interviews, code-review style polishing, and rehearsed explanations of complexity and tradeoffs. Focus your last-mile prep on writing correct, readable code quickly and on explaining why your solution is robust and efficient for production scenarios.
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Find shared objects across two log files
You are given two large log files representing activity on two different days. Each line of each log has three fields: - timestamp: a time value (you ...
Build a BFS Web Crawler
Implement a web crawler for a single website. You are given: - A starting URL startUrl - A function fetch(url) that returns the HTML content of a page...
Design set with O(1) random access
Design a data structure ("FancySet") that stores unique integers and supports the following operations, each in average O(1) time: - add(x): Insert va...
Determine winner in optimal-play card game
Given a row of N cards with integer values (values may be positive, zero, or negative), two players alternately pick either the leftmost or rightmost ...
Implement Ultimate Tic-Tac-Toe
Design and implement a playable Tic-Tac-Toe system in two parts. Part 1: Standard Tic-Tac-Toe Implement a TicTacToe class for a standard 3x3 board. Re...
Implement classes in existing abstract hierarchy
You are given an existing Python codebase that defines multiple classes, including abstract base classes using abc.ABC and @abstractmethod decorators....
Minimize deaths in spreading plant infection
You are given an m x n grid representing a garden: - 0: empty cell - 1: healthy plant - 2: infected plant The garden evolves day by day in the followi...
Write an average-income function
Given a Python list of dictionaries such as: records = [{"name": "a", "income": 100}, {"name": "b", "income": None}, {"name": "a", "income": 200}] Wri...
Implement a Batch Image Processor
Implement a program that applies basic image transformations to a batch of images. You are given a list of input image paths and, for each image, a se...
Implement a CSAT Sliding Window Tracker
Design and implement a class that tracks customer satisfaction scores over a sliding time window. A customer support conversation has: - conversation_...
Implement Stock Price Query APIs
You are given an initial collection of stock price records. Each record contains: - symbol: a stock name or ticker string - timestamp: initially a cal...
Design an Editable Text Buffer
The interview question was asked in three progressive stages. Design an in-memory text editor. 1. Basic text buffer Implement a data structure that ...
Check if all substrings are dictionary words
You are given a string s (letters only) and access to an English dictionary dict (a set of valid words). Return true if every contiguous substring of ...
Implement a stack supporting max and popMax
Design a data structure that behaves like a stack but also supports retrieving and removing the current maximum value. Implement a class MaxStack with...
Solve Adjacent-Deletion and Sorted-Square Problems
Solve the following coding problems. Discuss the approach and complexity before implementation. Problem 1: Remove adjacent duplicate pairs Given a str...
Solve three OA coding questions
You are given a 90-minute online assessment containing three coding questions. Implement solutions for all questions. --- Question 1: Group strings th...
Solve shipping capacity and expression insertion
Problem A: Minimum shipping capacity You are given an array weights where weights[i] is the weight of the i-th package. Packages must be shipped in or...
Count anagram-based replacements per phrase
Problem You are given: - phrases: a list of strings, where each string is a phrase containing words separated by single spaces. - words: a list of str...
Implement weighted random city and sparse dot product
Question 1: Weighted random city picker You are given a mapping from city → population (all populations are positive integers). Implement a random gen...
Optimize Trapping Rain Water
Question LeetCode 42. Trapping Rain Water – implement a brute-force solution, analyze its complexity, then optimize to an O(n) solution with O(n) spac...