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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Validate an IPv4 address string
Given a string s, determine whether it is a valid IPv4 address. A valid IPv4 address: - Has exactly 4 parts separated by dots (.): x1.x2.x3.x4 - Each ...
Design command executor with undo
This question evaluates understanding of the command pattern, state and history management, failure handling, and appropriate data structure use for i...
Build a Least-Recently-Used Store
Implement an in-memory key-value store with least-recently-used eviction. The store is initialized with a positive integer capacity and supports two o...
Compute Nearest Destination Distances
This question evaluates graph and grid traversal concepts, specifically multi-source shortest-path computation on a grid and handling special-cell con...
Count Trips From Vehicle Logs
You are given a text log of vehicle events on a road system. Each log record contains: - license_plate: a string identifying a vehicle - event_type: o...
Track Users From Flight History
You are given an unsorted list of flight records. Each record contains departure_airport, departure_time, arrival_airport, arrival_time, and user_id. ...
Explain list vs tuple in Python
This question evaluates understanding of Python sequence types, specifically differences in mutability, hashing ability, memory footprint, and iterati...
Find Shortest Queue with Few Calls
This question evaluates algorithm design and analysis skills, focusing on working with restricted data structure APIs and minimizing total operations ...
Generate unique permutations with duplicates
Given an array of integers that may contain duplicates, generate all unique permutations. Ensure no duplicate permutations are returned even if some v...
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...
Count decodings of a numeric string
Given a string s of digits representing an encoded message where '1' maps to 'A', ..., '26' maps to 'Z', and '0' cannot appear alone (it must be part ...
Implement tree traversals, BFS, and subsets generation
1) Define a TreeNode class for a binary tree with an integer value and left/right pointers. Implement preorder, inorder, and postorder traversals: (a)...
Maintain real-time top-K products from events
Design a data structure/class that ingests a stream of product events and returns the current top‑K products at any time. Events include {timestamp, p...
Devise sequence-rule detection strategy
You are given an integer sequence with 2 ≤ n ≤ 50 terms, possibly following rules such as arithmetic/geometric progressions, alternating patterns, pol...
Implement robust debounce and throttle in JavaScript
Implement debounce(fn, wait, options) and throttle(fn, wait, options) in JavaScript. Support leading/trailing invocation toggles, maxWait for throttle...
Implement GPU credit ledger
You manage a GPU pool with per-tenant credits. Given a list/stream of events where each event adjusts a tenant’s credit balance by a signed integer (p...
Find mode or minimum with time-space tradeoffs
For an unsorted array of integers, implement two functions: ( 1) return the minimum value; ( 2) return the value that appears most frequently (the mod...
Design a contiguous segment allocator
Design an in-memory contiguous segment allocator over an array of n cells (indexed 0..n- 1), all initially free. Support two operations: 1) allocate(l...
Design a queue and analyze tradeoffs
Design a FIFO queue data structure that supports enqueue, dequeue, peek, and isEmpty. Compare implementations using a singly linked list, a dynamic ar...
Clone list with random pointers
Question You are given the head of a singly linked list where each node has two pointers: next and random. The random pointer may be null or point to ...