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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Solve OA tasks on string, grid path, subarrays
You are given three independent coding tasks. Task 1: Reverse the middle if ends are vowels Given a string s (ASCII letters), if both the first and la...
Determine Whether a Word Exists in a Graph
You are given a graph as a list of node objects. Each node contains a character and a list of neighboring nodes that can be visited next. Design and i...
Solve Array Distance and Wiki Navigation
You are given two independent coding tasks. For each task, clarify edge cases, implement the function, and write meaningful test cases. Task 1: Minimu...
Compute letter frequencies from encoded string
Problem You are given an encoded string s representing a string of lowercase English letters (a–z). The encoding follows these rules: 1. Letters a to ...
Solve Stack and String Shift Problems
You are asked to solve two independent coding problems. Problem 1: Validate Delimiter Pairs Given a string s containing only the characters (, ), {, }...
Simulate Transaction Lock Scheduling
Implement an in-memory transaction lock simulator. You do not need to create real threads; you only need to simulate how transactions acquire locks, b...
Implement a Simplified DNS Resolver
Implement a simplified DNS resolver in Python. You are given an in-memory DNS zone and must complete a small resolver step by step. The goal is not to...
In-Memory File System: Create, Track Duplicates, and List
In-Memory File System: Create, Track Duplicates, and List Implement an in-memory file system that supports creating files and folders and listing the ...
Grid Robot Command Simulator
Grid Robot Command Simulator You are building a small command-driven robot simulator. A single robot lives on a 2D grid and is controlled by a stream ...
Implement cursor-based query pagination
You are building a small in-memory database that stores rows with the following fields: - id (string, unique) - score (integer) - payload (string) You...
Design a robot movement command system
Robot Movement (Pair Programming) You are given an empty starter repository (only a README). Implement a small, testable robot movement module that ca...
Determine balanced k values in a permutation
You are given a permutation p of the integers 1..n. For a number k (where 1 <= k <= n), call k balanced if there exists a contiguous subarray p[l..r] ...
Implement worker time and payroll tracker
You are building an in-memory worker management module. Each worker has metadata and a history of office attendance intervals. Implement the following...
Implement Social Follow Recommendations
Implement an in-memory social network graph with three operations: - follow(followerId, followeeId): record that one user follows another user. Duplic...
Implement Price-Time Order Matching
Implement a simplified limit-order matching engine for a stock exchange. You receive a stream of orders. Each order has: - order_id: unique identifier...
Partition a Target String by Source Substrings
You are given two strings: - target: the string that must be represented. - source: the string whose substrings may be used. Return a partition of tar...
Maximize coins with tokens moving by +3
You are given a 1D board represented by a string s of length n. Each character is one of: - '.' — an empty cell - 'C' — a cell containing exactly one ...
Streaming Entropy with Numerical Stability
Streaming Entropy with Numerical Stability You are processing a very large, possibly unbounded, stream of category labels (for example, token IDs emit...
Connect Points With Minimum Total Distance
You are given an array points, where points[i] = [xi, yi] represents a point on a 2D plane. The cost to connect two points i and j is their Manhattan ...
Traverse a tree and answer 2D prefix sums
You are given two independent coding tasks. Task 1: In-order traversal of a binary tree Given the root of a binary tree, return the in-order traversal...