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 Special Subarrays by Modular Frequency
You are given an integer array nums, and two integers modulo and target, where 0 <= target < modulo. Call an index i special if nums[i] % modulo == ta...
Design Algorithm to Minimize Payments in Expense-Sharing App
Scenario Expense-sharing app needs to settle debts among friends after a trip. Question Given a list of transactions (payer, payee, amount), design an...
Implement DelayQueue with Idempotent Task Execution
Scenario Message broker offers DelayQueue where tasks execute at future timestamps, ensuring idempotency on duplicate IDs. Question Implement a delay ...
Determine Pin Connections Through Common Boards
Scenario Pinterest boards contain many pins; need to infer relationships between pins. Question Given the membership lists of all boards, write a func...
Track Customer Referral Revenue
Design a data structure to track customers and referral-based revenue. Implement the following operations: - int insertNewCustomer(double revenue) -...
Implement Cache and Key-Value Store
The interview report mentions coding tasks similar to the following: 1. Bounded cache Implement a cache with a fixed capacity. Support: - get(ke...
Find conflicting pair using black-box run()
Problem You are given a list tests of n distinct test cases (you can treat them as IDs or objects). You also have access to a black-box function: - ru...
Find K most frequent elements
Problem You are given an array of integers nums and an integer k. Return the k elements that occur most frequently in nums. You may return the answer ...
Implement Three Research Coding Tasks
Solve the following coding problems. 1. Implement a differentiable matrix product You are given a list of k square matrices M1, M2, ..., Mk, all of sh...
Find dictionary words matching a phone digit string
You are given: - A digit string digits consisting of characters '2'–'9'. - A list of lowercase words words (dictionary). Use the classic phone keypad ...
Design an IPv4 Address Iterator
Design a class that iterates through IPv4 addresses. An IPv4 address is a string in the form a.b.c.d, where each octet is an integer from 0 to 255. Im...
Compute infection spread time
You are given an m x n grid representing a population during an outbreak: - 0 = empty cell - 1 = healthy person - 2 = infected person Every minute, ea...
Identify all bad nodes with group tests
You have N nodes. Each node is either good or bad (unknown to you). You can call a function test(S) on a subset of nodes S: - test(S) = True iff all n...
Convert an IP range to minimal CIDRs
Problem Given a starting IPv4 address ip and a non-negative integer n, output the smallest possible list of CIDR blocks that exactly covers n consecut...
Implement a Tic-Tac-Toe game API
Problem Design and implement a Tic-Tac-Toe game class that supports playing moves on an n x n board. Requirements - Two players, represented by intege...
Solve Anagram Without Sorting
Given two strings s and t, return true if t is an anagram of s, and false otherwise. You may not sort either string. An anagram uses exactly the same ...
Solve common search/parse/graph frequency tasks
You are given several independent coding tasks. For each task, write a function that returns the required output. 1) Find insertion index in a sorted ...
Solve three interview coding problems
This interview report described three coding tasks: 1. Generate a run-length spoken sequence Start with s1 = "1". To build the next term, read th...
Find shortest subarray with ≥k distinct integers
Given an integer array nums of length n and an integer k, find the length of the shortest contiguous subarray that contains at least k distinct intege...
Implement a Lazy Array
Implement a lazily evaluated array abstraction. The object should wrap an underlying sequence and support chained transformations such as map and filt...