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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Detect recurring transactions from a ledger
You are given a list of credit/debit card transactions. Each transaction has: - transaction_date (YYYY-MM-DD) - merchant (string) - amount (decimal, p...
Maximize min+max of contiguous subarray
You are given an array of n positive integers nums. Find a contiguous subarray that contains at least two elements and maximizes the value: > (minimum...
Rearrange array to maximize positive prefix sums
Problem You are given an integer array a of length n. You may rearrange the elements in any order. Define the prefix sums of a permutation p as: - pre...
Schedule Ready Tasks by Deadline
You are building a workflow scheduler. Each task has: - a unique task_id - an integer deadline - an optional list of prerequisite tasks that must be c...
Implement URL Shortening Codec
Implement a small in-memory URL-shortening component in a pair-programming interview. Expose two methods: shorten(long_url: str) -> str, which returns...
Implement Server Number Allocation
Implement a server number allocator for a data center. Servers have a string type, such as "web", "database", or "cache". Each server type has its own...
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...
Build a Friend Recommender
You are given a simple social-graph codebase where each user has only an id and a collection of current friends. Starting from existing functions and ...
Find tree root and bucket numbers
You are given two independent tasks. Task 1: Find the root of a tree from adjacency logs You are given an unordered list of records describing a roote...
Detect fraud events and extract PII
You are given a list of event objects (dictionaries/JSON). Each event has: - event_type: either "underwriting" or "fraud_flag" - customer_details: a n...
Compute minimum rooms for time intervals
You are given a list of meeting time intervals, where each interval is represented as [start, end) (start time inclusive, end time exclusive) and star...
Minimize coins with overpay and change
You have an unlimited number of coins with denominations: - 1, 5, 10, 50, 100, 200 You need to pay exactly n units to another person. You are allowed ...
Find top-k distinct elements
Given an integer array nums and an integer k, return the k largest distinct values from nums. Requirements - Values in the output must be distinct (no...
Implement a crypto order management system
You are building an in-memory crypto order management system. You must parse commands from standard input and print outputs for query commands. Order ...
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 minimum activations to absorb all balls
You are given n balls on a 2D plane, where ball i is at coordinate \((x_i, y_i)\). You are also given a distance threshold d. Two balls are considered...
Implement a type-based mutex for tasks
Problem You are given a multithreaded task runner. Each task has: - task_id: int - task_type: "gen" | "score" - duration: int (seconds) Each task runs...
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...