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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"I honestly don't know how you guys gather so many real interview questions. It's almost scary. I walked into my Amazon loop and recognized 3 out of 4 problems from your database."
"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."
Implement a Cloud Storage Service
Implement an in-memory cloud storage system. Build the class incrementally; later levels must preserve all behavior from earlier levels. File names ar...
Implement SQL Table and DNA Ordering
Two independent coding exercises were asked. Solve both. Problem A: CSV-backed in-memory table Build a tiny in-memory relational table initialized fro...
Count Nodes Using Asynchronous Messages
You are given the identifier of a root node in a distributed network. Each node represents a separate machine. A node cannot directly inspect another ...
Decode an encoded string
Implement a decoder for an encoded string where repetition is expressed with a number followed by a bracketed substring. Rules: - A pattern k[substrin...
Maximize palindromic strings after character swaps
You are given an integer n and an array of n lowercase strings arr. Operation (can be performed any number of times): choose two different strings arr...
Simulate turn-based monster team battle
Design an object-oriented model and implement the core battle logic for a turn-based fight between two teams of monsters. The system should simulate t...
Find all cells reachable by downhill flow
Problem You are given an m x n grid heights, where heights[r][c] is the elevation of cell (r, c). A drop of water is placed at a starting cell start =...
Determine Reachability in Train Schedule
You are given a train schedule represented as a list of train routes. Each route is a list of station names, where the element at index t is the stati...
Optimize password transform and discount scheduling
Part 1 — Transform to palindromic k-periodic string: Input: a lowercase string currentPassword and integer k. Constraints: 1 <= k < len(currentPasswor...
Move zeros to the front
You are given an integer array nums. Reorder the array in place so that all 0 values are moved to the beginning of the array, while preserving the rel...
Implement an article voting tracker
Coding: Article Voting Tracker Design and implement a data structure to track users’ votes (upvote/downvote) on articles. Operations Implement functio...
Count paths with prime-ending jumps
You are given an integer n representing the top of a staircase, where you start at step 0 and want to land exactly on step n. In one move, you may jum...
Solve Stack Decoding and Fuel-Constrained Paths
You are given two independent coding tasks. Task 1: Decode a Repeated-Pattern String Given a valid encoded string, return its fully decoded form. The ...
Implement KV Store and Token Bucket
The coding portion covered two implementation tasks: 1. Implement a simple in-memory key-value store. Support basic operations such as: - put(key, val...
Find Duplicate Files
Implement a file deduplication tool. You are given a root directory containing many files. Return groups of duplicate files. Two files are duplicates ...
Find Shortest Paths to Target Nodes
You are given a weighted directed graph representing distances between nodes. - There are n nodes labeled from 0 to n - 1. - edges[i] = [u, v, w] mean...
Schedule Incremental Labeling Tasks
You are building a data-labeling platform. Each day, a batch of task IDs arrives. A task ID may reappear on later days because the platform may reques...
Sum palindrome-change costs over all substrings
You are given a DNA string dna consisting only of characters A, C, G, T. For any substring dna[l..r], define its palindrome modification cost as the m...
Compute peak parking lot occupancy intervals
You are given logs from a parking lot system. Each log entry has the form: [carId, time, eventType] - carId is an integer identifying a car. - time is...
Implement an In-Memory File System
Design an in-memory file system that supports file management, search, user ownership, capacity limits, copying, and compression. Each file has a uniq...