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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Count islands using BFS without modifying grid
You are given an m x n binary grid grid where: - 1 represents land - 0 represents water - Islands are groups of horizontally or vertically adjacent la...
Match payments to invoices by memo or amount
You are building a small payment-to-invoice matching utility. Data You are given: - invoices: a list of invoice records with: - invoice_id (string) ...
Find first and last index of target
You are given an integer array nums sorted in non-decreasing order and an integer target. Return a pair [left, right] where: - left is the index of th...
Write SQL to rank top products per category
You are given two tables: products - product_id (int, primary key) - category (string) order_items - order_id (int) - product_id (int) - quantity (int...
Find path between two nodes in a binary tree
Problem Given a binary tree and two target nodes a and b, return the simple path from a to b (inclusive) as an ordered list of node values. - The path...
Generate All Valid Combinations of Balanced Parentheses
Generate All Valid Combinations of Balanced Parentheses Given an integer n representing the number of pairs of parentheses, generate all distinct stri...
Implement a type-erased function wrapper
Implement a minimal std::function-like callable wrapper in C++ using type erasure via inheritance and a virtual call. Define a template Function<R(Arg...
Implement flat_map and design wealth redistribution
Part 1 — Implement a flat_map: Design and implement an associative container flat_map backed by a sorted dynamic array of (Key, Value) pairs. Support ...
Minimize steps to reduce integer
Given a positive integer n (1 <= n <= 2^61 - 1), in one step you may replace n with n/2 if n is even, or with n+1 or n-1 if n is odd. Return the minim...
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...
Search a word in a grid
Given a 2D grid of characters and a target word, determine if the word can be traced by moving up, down, left, or right, using each cell at most once....
Solve string dictionary and tree ordering
Part A — One-edit dictionary: Build a data structure supporting build(words: List[str]) and search(query: str) -> bool that returns true if and only i...
Design a transactional in-memory key–value store
Implement an in-memory key–value store that supports transactions. The system must process these commands: ( 1) SET key value — assign or overwrite a ...
Count user sessions from logs
Given a large log file where each line is "timestamp,user,action", compute the number of sessions per user. Assume a session ends if the gap between c...
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...
Optimize with a cache/hash map
Question This is a follow-up to your existing implementation (for example, a script that repeatedly resolves file paths or parses license strings into...
Find leftmost point of maximum brightness
You are given an array of lights, where each light is [p, r] representing a lamp centered at coordinate p on the real number line with radius r, illum...
Implement 2D transforms and find max-lit point
Part A — 2D array transforms: Given an m×n integer matrix, implement the following in-place operations with clear function boundaries and complexity: ...
Design a balloon stability tracker
Implement a class BalloonFestival to manage hot-air balloons and wind fields over time, and to report rewarded balloons at inspection times. Methods a...
Solve Signature, File, and Queue Problems
Solve the following interview-style problems: 1. Function signature matching You are given a registry of function definitions. Each function has an...