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 ways to make change (DP)
Problem You are given an integer amount and an array of positive, distinct integers coins, where each coin value can be used unlimited times. Return t...
Schedule prerequisite classes with retakes
Problem You are building a course-taking engine. Each course is represented as an object: - id (unique identifier) - prevCoursesList: a list of prereq...
Find the third-largest word by length
Given an array of strings strArr (length ≥ 3), return the third largest word when ranking words by string length in descending order. Ranking rules: -...
Implement a hash table with put/get
Problem Implement a simplified hash table (hash map) data structure from scratch. Required API Design a class HashTable with: - HashTable(int numBucke...
Implement local maxima, bagging, and k-means
You have 70 minutes for three programming tasks. Task 1 — Find local maxima Given an integer array a of length n (1 <= n <= 2e5), return all indices i...
Move zeros to the front
Given an integer array nums, move all elements equal to 0 to the beginning of the array while preserving the relative order of all non-zero elements. ...
Complete decision tree and gradient descent functions
You are given partially implemented code and must complete key functions. Implement the missing parts with correct logic and reasonable efficiency. Ta...
Compute moving average over last N stream
You are given an integer N and an unbounded stream of integers arriving one by one. After each new integer arrives, output the average of the last N i...
Generate constrained NFT metadata
Given a set of trait types (e.g., background, eyes, hat), each with a list of allowed values, and a target count N, implement a function to generate N...
Count clusters covered by dashers
You are given two m×n binary matrices of equal size: D for dasher availability and U for user presence. A cell value 1 indicates presence; 0 indicates...
Solve two algorithm problems from a menu
Choose two problems from an algorithms menu (arrays, strings, hash maps, graphs). For each: 1) state clarifying assumptions, 2) implement a correct so...
Explain hash maps and solve array intersection
1) Explain the internal implementation of a hash map: underlying array/bucket layout, hash function choice, collision resolution strategies (separate ...
Implement rotating homepage title selector
Implement an in-memory service that chooses which movie or show title to display on a user's homepage billboard. Each title has a relevance score for ...
Implement an expiring counter class
Expiring Counter (sliding time window) Design and implement an expiring counter that counts events in a recent time window. Requirements - You are giv...
Answer parity-alternation range queries
You are given an integer array nums of length n and q queries. Each query is a pair [l, r] (0-indexed, inclusive). A subarray nums[l..r] is called alt...
Match payments to invoices with fallback rules
You are given two datasets: - invoices: each invoice has invoice_id, date, amount - payments: each payment has payment_id, optional invoice_id (may be...
Solve Merge Lists and Vertical Traversal
Two coding tasks were mentioned for a 40-minute round: 1. Merge multiple sorted linked lists: You are given an array of k singly linked lists, where e...
Aggregate user logs into 30-minute sessions
You are given a CSV file with columns: user_id | log_datetime | topic Example input rows (already in time order for the same user): - 001 | 2025-03-01...
Implement Euclidean distance and k-nearest neighbors
You are working with points in an n-dimensional Euclidean space, where each point is represented as a list (or array) of numeric coordinates. Assume: ...
Implement Depth-First Search Traversal
Given a graph represented as an adjacency list and a starting node, write a depth-first search function that returns the nodes visited in DFS order. Y...