Coding & Algorithms Interview Questions
Practice 3,469 real Coding & Algorithms interview questions for 2026. Covers companies like Meta, Amazon, Google, Uber, and Microsoft. Real questions from actual interviews with detailed solutions — ideal for focused interview preparation. Coding & Algorithms interview questions are the single most common technical gate for software engineering roles and are used to evaluate problem framing, algorithm selection, complexity trade-offs, correctness, edge-case reasoning, and clear communication under time pressure. Expect this category to appear in early technical screens and repeatedly across onsite loops at companies that weight it heavily (notably Meta, Google, and Amazon). Interviews will test arrays and strings, trees and graphs, dynamic programming, hashing and two‑pointer techniques, and the candidate’s ability to test and optimize code in a shared editor. Prepare with timed mock interviews, practice in the same editor you’ll use live, and build a progressive schedule that moves from fundamentals to medium/hard problems; typical candidates invest several weeks to a few months of focused practice depending on seniority and target company.
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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."
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Debug and optimize a card-drawing strategy
This question evaluates debugging and implementation skills, combinatorial search and optimization, and the ability to design and interpret simulation...
Simulate sticky load balancer with shutdown
Problem Implement a simulator for a load balancer that routes long-lived WebSocket connections across m backend servers. You receive a sequence of tex...
Solve Three Algorithm Variants
You are given three independent coding problems. For each one, describe and implement an efficient solution. 1. Generate queue arrangements - You a...
Implement an in-memory key-field-value DB with TTL
In-Memory DB with TTL + Scan + Backup/Restore Implement an in-memory database storing records by (key, field) -> value with optional TTL. Data model /...
Solve powers, phases, grid pops, and swaps
Solve the following four problems: 1) Count powers of k in an array: Given an array of positive integers nums and an integer k >= 1, return how many e...
Simulate Grid Infection
This question evaluates skills in multi-source breadth-first search, synchronous simulation updates, boundary handling, and off-by-one correctness wit...
Level-Ordered Dependency Build Order
This question evaluates a candidate's ability to model dependency relationships as a graph and produce a valid topological build order. It tests knowl...
Multi-Agent Collision Simulator (Unicycle Kinematics)
This question tests practical coding ability in robotics simulation, specifically implementing unicycle kinematics and discrete-time modeling via forw...
Implement a CSV dataset join
Implement joinDataSet(fieldName, customerFile, processorFile, skipUnmatched). You are given two datasets represented as List<String>, where: - custome...
Find Shortest Paths in Road Network
You are reviewing code for a road-network graph. The domain objects are: `java class Location { String name; Location(String name) { this.name...
Implement K-means clustering from scratch
This question evaluates a candidate's understanding of clustering algorithms and practical implementation skills in unsupervised machine learning, inc...
Simulate Infection Spread on a Grid
This question evaluates the ability to implement and reason about discrete-time, grid-based simulations with multi-state cells and neighbor-dependent ...
Implement a snapshotable set with iterators
Implement a SnapshotSet data structure with the following API: add(x), remove(x), contains(x), snapshot() -> sid, and iterate(sid) -> iterator over th...
Design O(1) Randomized Multiset
This question evaluates data-structure design skills, understanding of hashing and randomization for uniform sampling, handling of duplicate elements,...
Longest Substring Without Repeating Characters
This question tests a software engineer's ability to apply sliding window techniques and string manipulation to optimize character uniqueness tracking...
Course Schedule Feasibility
This question tests graph traversal skills and the ability to detect cycles in a directed graph, a core competency in algorithm interviews. It falls u...
Implement bus route simulation features
Bus Route Simulation – Boarding, Capacity, and Priority Passes You are given a partially implemented codebase for simulating bus routes in a city. Bus...
Implement 3x3 matrix transforms and rotation
Implement 3x3 matrix transforms and rotation For a 3x3 matrix, write Python code to: (a) transpose it in-place; (b) swap any two rows and any two colu...
Implement Social Follow Recommendations
This question evaluates graph data structure design and traversal, set-based aggregation and ranking logic, and the ability to justify data structure ...
Resolve routing-number to bank mapping
You are given bank-routing data coming from one or more JSON sources. Each source provides a list of records like: `json { "routing": "026009593", "ba...