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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Enforce ordered execution across threads
Implement a class with three methods alpha(), beta(), and gamma() that may be called by three different threads in arbitrary order, but must print the...
Design streaming stats with sliding window
Design a data structure that ingests an integer stream and supports online queries for maximum, mean, and mode. 1) Describe your update and query oper...
Validate course catalog dependencies
Design a function to validate an e-learning course catalog. You are given: ( 1) a set of course IDs, and ( 2) a list of prerequisite pairs (u, v) mean...
Sample index from probability distribution
You are given a discrete probability distribution for an \(M\)-sided die as an array p[0..M-1], where each p[i] is non-negative. Design a function sam...
Validate parent array forms a tree
Problem You are given an integer array parent of length n describing a directed parent pointer for each node i (nodes are labeled 0..n-1). - parent[i]...
Find user who can access every camera
You are given permissions data describing which users and groups have ownership access to which cameras, and which entities are members of which group...
Solve three array/string/graph coding tasks
You are given three separate coding tasks. Implement each as a function. 1) Merge three sorted arrays Input: Three integer arrays A, B, C, each sorted...
Extend a BFS maze solver stepwise
Maze Solver (4 incremental tasks) You are given an existing codebase for a maze solver that finds a path in a 2D grid. The maze is represented as a re...
Implement a single-thread task scheduler API
Design and implement a simple task scheduler for a single CPU, single thread environment. You need to support scheduling callbacks (tasks) using the f...
Implement sliding-window moving average
Design a class MovingAverage that supports a constructor MovingAverage(k) and a method next(val) returning the average of the last k values from a dat...
Parse and evaluate nested expressions with validation
Design and implement a parser/evaluator for a parenthesized expression language where the input string may be invalid. The language uses spaces as tok...
Merge two sorted linked lists
Given the heads of two singly linked lists sorted in non-decreasing order, merge them into a single sorted singly linked list and return its head. Imp...
Find palindrome-forming string pairs
Given an array of distinct lowercase strings words, return all index pairs (i, j) with i != j such that the concatenation words[i] + words[j] is a pal...
Implement string matching with follow-up
Question Given a text T and a pattern P, implement a function firstIndex(T, P) that returns the starting index of the first occurrence of P in T, or -...
Compute and optimize average wait time
You are given n pickup orders for a grocery delivery counter. Each order i is described by orders[i] = [arrival_i, service_i] in minutes, where arriva...
Implement Disease and Friend Snapshot Models
You are asked to solve two independent coding problems. Problem 1: Simulate disease spread on a contact graph There are n people labeled 0 through n -...
Solve Five Coding Problems
The interview included several coding tasks. Solve each of the following and discuss time and space complexity: 1. Given a 2D grid where '1' represent...
Implement KNN from Scratch
Implement a k-nearest neighbors (KNN) classifier from scratch in Python without using scikit-learn's KNN implementation. Given training features X_tra...
Implement in-memory DB querying
Question Implement an in-memory database that supports: 1. Querying the whole table and returning only selected columns (projection). 2. Adding WHERE ...
Implement cloud storage with quotas and compression
Problem Implement an in-memory cloud storage service that supports multiple users, per-user storage quotas, changing quotas with eviction, and file co...