Coding & Algorithms Interview Questions
Practice 3,013 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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Determine winner in stack-merging game
Game: Babylon stack merging (two-player, perfect play) You are given a two-player turn-based game. There are n stacks of tiles. Each stack has: - a he...
Reconstruct original array from doubled shuffle
Problem You are given an integer array changed that was produced from some unknown integer array original using the following process: 1. Start with o...
Count completed car journeys from sensor logs
You are given a time-ordered list of highway sensor logs. Each log entry contains: - timestamp (integer; strictly increasing) - sensor_type (one of "E...
Compute tree right view and target-sum subarrays
You are given two separate programming tasks. --- Task 1: Right-side view of a binary tree You are given the root of a binary tree. Imagine standing o...
Refactor a chat message processing function
Task You are given a poorly written JavaScript function that processes an incoming chat message and updates an in-memory store. The code is hard to re...
Validate Password Against Multiple Rules
Implement a password validation function for an account security system. You are given: - a string password - an integer min_length - a set of forbidd...
Check if each recipe is a contiguous subsequence
You are given: - An ordered ingredient list ingredients[0..n-1]. - A list of m recipes. Each recipe recipes[j] is itself a list of ingredients and is ...
Break a palindrome to smallest non-palindrome
Given a palindromic string s of lowercase English letters, change exactly one character to obtain a new string that is not a palindrome and is lexicog...
Implement classes within an abstract Python framework
You are given an existing Python codebase (~200 lines shown) that defines an abstract base class DataProcessor with abstract methods load(self), trans...
Implement a nested key-value store
Design and implement a nested key–value store that supports set(path, value), get(path), and delete(path), where path is dot-delimited (e.g., "a.b.c")...
Compute peak concurrent drivers in 24 hours
Given delivery intervals across multiple drivers, compute the maximum number of distinct drivers simultaneously active within the last 24 hours from a...
Implement queue-based rate limiter with multi-key limits
Implement a rate limiter with method allow(timestamp) that returns true if a request is allowed under a limit of K requests per rolling window W milli...
Simulate stack traces from logs
Given a list of log entries describing function calls, each formatted as "<id> <event> <timestamp>" where event ∈ {START, END} and timestamps are inte...
Find word sequence with 1–2 char changes
Given a beginWord, an endWord, and a dictionary (wordList) of unique same-length lowercase words, determine whether there exists a transformation sequ...
Implement a recency-eviction bounded cache
Implement an in-memory key–value store with a fixed capacity N that uses recency-based eviction. Support: get(key) -> value or -1 if missing, and put(...
Differentiate Java final, finalize, finally
Differentiate Java's final, finalize, and finally. Define what final means for variables, methods, and classes and give examples; explain what finaliz...
Compute optimal matrix multiplication order
Given an array dims[0..n] where matrix i has dimensions dims[i-1] × dims[i] (for i = 1..n), compute the minimum number of scalar multiplications neede...
Solve and optimize menu combo DP
Given up to N different menu items, each with a unit price, and a list of combo offers where each offer specifies quantities for some items and a tota...
Pass functions and analyze basic data structures
Implement a function applyTwice(f, x) that accepts a function f and a value x and returns f(f(x)) in your preferred language. Demonstrate how to pass ...
Find returning users from access logs
Given an unordered log of web access events, identify which users are returning (i.e., they have visited on at least two different calendar days). Eac...