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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"Discovered PracHub 10 days before my interview. By day 5, I stopped being nervous. By interview day, I was actually excited to show what I knew."
"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
"The search is what sold me. I typed in a really niche DP problem I got asked last year and it actually came up, full breakdown and everything. These guys are clearly updating it constantly."
Design a max-stack with efficient operations
Design a stack that supports push (x), pop(), top(), peekMax(), and popMax(). The popMax operation must remove and return the maximum element; if ther...
Determine string segmentability with dictionary
Given a string s and a dictionary of words, determine whether s can be segmented into a sequence of dictionary words. Provide a dynamic-programming so...
Implement in-memory KV store with serialization
Implement an in-memory key-value store in Python that supports setting and retrieving values and can serialize and deserialize the entire store. Defin...
Count expressions reaching a target sum
Given an array of non-negative integers nums and an integer target T, assign either a + or − sign to each number to form an expression. Count how many...
Explain AtomicInteger and ABA problem
How does AtomicInteger implement atomic updates (e.g., via CAS using Unsafe or VarHandles)? What is the ABA problem in lock-free algorithms, how can i...
Solve classic backend coding problems
Solve the following coding problems. 1. Find the missing number from a concatenated range You are given an integer n and a string s. The string was fo...
Find missing value in sorted consecutive array
Given a sorted array nums of distinct integers. The numbers are supposed to form a consecutive sequence starting from some unknown integer start: - If...
Find user pairs with overlapping last K movies
You are given the same user movie-watching histories as in the previous problem. Each user’s history is an ordered list of movie IDs from earliest to ...
Compute clock hand angle with seconds and milliseconds
You are given a time in the format "HH:MM", representing a 24-hour clock time with hours and minutes. Extend this to potentially include seconds and m...
Design data structure similar to LRU cache
You are asked to design and implement a data structure that behaves similarly to an LRU (Least Recently Used) cache, but with a small variation: - The...
Compute balances and array queries
Question Given a list of transactions where each transaction has a userId and an amount (positive for credit, negative for debit), compute the final b...
Implement test failure analytics APIs
Question Design a data structure that supports: log(testId, timestamp, status) — record the status ('pass'/'fail') of a test run; timestamps are stric...
Compute drawdown, profit, and coin change
Question What is the maximum drawdown of a cumulative PnL (profit and loss) series, and when did it occur? Implement a function mdd(pnl) that returns ...
Compute delay times in priority array
Question Given an array of integers representing task priorities processed from right to left, return an array where each element is the distance (ind...
Find LCA in organization tree
Question Given an organizational hierarchy tree, return the lowest common organization (parent node) for two or more employees (≥ 2). Provide unit tes...
Maximize path score in DAG
Question Given a weighted directed acyclic graph (DAG) where each node v has a score w(v) and each edge (u→v) has a time cost t(u,v), starting from no...
Solve Logic Puzzles: Algorithms and Proofs Required
Scenario On-site logic/algorithm quiz with hiring manager and VP Question Solve six AMC-8–level math/logic puzzles, including the classic farmer-fox-c...
Generate Bigrams Using Python List Comprehension and Zip
Scenario Live Python exercise: generate all bigrams from an input string and iteratively optimize the solution. Question Write a Python function that ...
Solve Algorithmic Challenges in Online Coding Assessments
Scenario Online assessment requiring implementation of common algorithmic problems. Question Given an array of integers and a target, return indices o...
Implement Prefix Match Filter
Design a data structure that stores a collection of prefix strings. Then, given a list of input strings, return every string that begins with at least...