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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"Discovered PracHub 10 days before my interview. By day 5, I stopped being nervous. By interview day, I was actually excited to show what I knew."

"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
"The search is what sold me. I typed in a really niche DP problem I got asked last year and it actually came up, full breakdown and everything. These guys are clearly updating it constantly."
Compute delivery order via BFS
A city road network is an unweighted, undirected graph G(V, E) with a depot node s and D delivery requests located at nodes r1..rD, each with an integ...
Implement an In-Memory Database
Design and implement an in-memory database that stores records by key. Each record is a map from field to integer value. Implement the following funct...
Implement Trie search with wildcard matching
Design a text dictionary using a Trie. Support the following operations: - addWord(word): Insert a lowercase English word. - search(pattern): Return t...
Determine if a multiple-sum subarray exists
Given an integer array nums and an integer k, determine whether there exists a contiguous subarray of length at least 2 whose sum is divisible by k; r...
Count vowel-only substrings with all vowels
Given a lowercase English string s, return the number of contiguous substrings that ( 1) consist only of vowels from the set {a, e, i, o, u}, and ( 2)...
Implement LRU cache with O(1) ops
Design and implement a fixed-capacity cache supporting get(key) -> value and put(key, value) in O( 1) average time. When capacity is reached, evict th...
Calculate Courier Earnings
Design a function to calculate total courier pay from a set of delivery orders. Assume time is represented as integer minutes, and intervals are half-...
Implement a memory allocator with malloc/free
Problem You are implementing a simplified memory allocator over a contiguous memory region. Initialize the allocator with a fixed total size: - alloca...
Implement Kac ring with O(1) color and kstep
You are implementing a Kac ring dynamical system. Model - There are N positions arranged in a circle, indexed clockwise: 0, 1, ..., N-1. - Each positi...
Traverse org chart level by level
Problem You are given an organization chart as manager relationships. Each employee is represented by: - employee_id (string/int) - manager_id (string...
Maximize profit with transaction fee
Given an array of daily stock prices and a fixed transaction fee charged on each sell, compute the maximum profit achievable with any number of buy–se...
Implement log aggregation in React
React Coding: Log stream aggregation You are building a small React feature that displays real-time statistics from a log stream. Log event format Eac...
Solve Several Algorithm Problems
The interview included several coding tasks: 1. Longest symmetric substring: Given a string s, return the longest contiguous substring that reads the ...
Maximize Unique Characters from Words
You are given a list of lowercase English words. Select a subset of the words such that no character appears more than once across all selected words....
Implement K-means clustering from scratch
Task: Implement K-means clustering (from scratch) Write a function to perform K-means clustering on a set of points. Input - A dataset X with shape (n...
Filter Invalid Data Events
You are given a list of data events. Each event contains: - event_id: string - creator_id: string - event_type: string - event_time: Unix timestamp - ...
Parse a protobuf-like schema and answer queries
You are given a single string schema describing message types in a simplified, protobuf-like language. Your task is to parse the schema and support tw...
Implement recent-requests counter
You are designing an in-memory component for a web service that needs to track how many requests ("hits") it has received in the last 5 minutes. Imple...
Compute trigger counts in a DAG
You are given a directed acyclic graph (DAG) that represents trigger dependencies between tasks. - Each node represents a task. - There is exactly one...
Group users by same last K watched movies
You are given a list of users' movie-watching histories. Each user’s history is an ordered list of movie IDs in the order they were watched (earliest ...