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LeetCode
View on WikipediaLeetCode is an online platform for coding interview preparation. The platform provides coding and algorithmic problems intended for users to practice coding.[3] LeetCode has gained popularity among job seekers in the software industry and coding enthusiasts as a resource for technical interviews and coding competitions.[3][4][5][6][7] As of 2025, the website has 26.3 million monthly visitors.[8]
Key Information
Features
[edit]LeetCode offers both free and premium access options. While free users have access to a limited number of questions, premium users gain access to additional questions previously used in interviews at large tech companies.[3] The performance of users' solutions is evaluated based on execution speed and memory usage, and is ranked against other submissions in the LeetCode database.[9]
Additionally, LeetCode provides its users with mock interviews and online assessments. LeetCode hosts weekly and biweekly contests, each having 4 problems.[6][10] After participating in a contest for the first time, one gets assigned a ranking, which can be found in their profile.[11] LeetCode also provides its users with daily challenges, following UTC, with a lucky draw at the end of each month for those who stayed consistent for the month.[12]
LeetCode supports a wide range of programming languages, including Java, Python, JavaScript, and C.[13] In September 2024, LeetCode China supports Huawei's Cangjie programming language for all problems.[14]
The platform features forums where users can engage in discussions related to problems, the interview process, and share their interview experiences.[6]
Types of problems
[edit]Every question on LeetCode has a particular category or tag. Some of the most common tags include arrays, strings, two pointers, stacks, binary search, sliding windows, linked lists, trees, tries, backtracking, heaps, priority queues, graphs, breadth-first search, depth-first search, dynamic programming, greedy algorithms, bit manipulation, database problems, and math.[15][better source needed] As of April 2025, LeetCode offers 3525 questions across its three levels of difficulty; with 873 questions categorized as easy, 1829 as medium, and 823 as hard.[10][better source needed]
History
[edit]LeetCode was founded in Silicon Valley in 2015 by Winston Tang.[16][17] After moving to the US from Malaysia in 2005, Tang founded the company, citing his own experiences working at Amazon and Google as inspiration.[17][18]
LeetCode expanded its operations to China in 2018, providing Chinese problems, solutions and forums on its Chinese website Likou (Chinese: 力扣; pinyin: Lìkòu).[19] In 2021, LeetCode secured its first round of funding, receiving a $10 million investment from Lightspeed China Partners.[19]
See also
[edit]References
[edit]- ^ LeetCode: Contact Details, Revenue, Funding, Employees and Company Profile Silicon Valley Journal
- ^ LeetCode Employee Directory, Headcount & Staff LeadIQ
- ^ a b c Singer, Natasha (2023-04-05). "For Lower-Income Students, Big Tech Internships Can Be Hard to Get". The New York Times. Retrieved 2023-08-09.
To gear up for the assessments, many students practice their skills on LeetCode, a free test prep site that offers coding and algorithmic problems, along with detailed solutions. The site also offers premium services. For $35 a month, it gives members access to specific problems that companies like Amazon, Google and Microsoft previously used — and some continue to use — to assess applicants. To keep the questions up-to-date, the test prep service said, it regularly surveys members applying for tech positions.
- ^ Ansari, Tasmia (2022-11-17). "The Ultimate Guide to Cracking Data Science Interviews". Analytics India Magazine. Retrieved 2023-06-10.
- ^ Kolakowski, Nick (2022-12-08). "Which Programming Languages Are Growing?". Dice Insights. Retrieved 2023-06-10.
- ^ a b c Sonmez, John; Butow, Eric (2019-09-11). Programming Interviews For Dummies. John Wiley & Sons. ISBN 978-1-119-56506-2.
LeetCode is also a popular site for programmers who want to get up to speed.
- ^ Harper, Jocelyn (2023), Harper, Jocelyn (ed.), "Interview Insight: How to Get the Job", A Software Engineer's Guide to Seniority: A Guide to Technical Leadership, Berkeley, CA: Apress, pp. 19–28, doi:10.1007/978-1-4842-8783-5_4, ISBN 978-1-4842-8783-5, retrieved 2023-08-11,
LeetCode is a platform that specializes in algorithm questions ranked from "Easy" to "Hard" based on the complexity of the subject and solution. They also have a forum where people share what interview questions they encountered in phone screens and on-site interviews to share with the larger public and to help software engineers prepare. I have been fortunate that the only time that I encountered a LeetCode problem during a screening process was for Amazon. ... On this last interviewing journey, I found myself enjoying practicing algorithm coding questions because I found alternative resources to LeetCode.
- ^ leetcode.com Traffic analytics, ranking & audience (May 2025) Similarweb
- ^ Xing, Jessica. "Here's what job seekers need to know about LeetCode, the coding-skills platform millions of developers use to ace the notoriously difficult technical interviews at firms such as Apple, Amazon, and Google". Business Insider. Retrieved 2023-06-21.
- ^ a b "LeetCode - The World's Leading Online Programming Learning Platform". leetcode.com. Retrieved 2023-10-10.
- ^ "Contest". LeetCode. Retrieved 2023-10-10.
- ^ "What is Daily LeetCoding Challenge?". leetcode.com. Retrieved 2023-12-09.
- ^ Nguyen, Nhan; Nadi, Sarah (2022-10-17). "An empirical evaluation of GitHub copilot's code suggestions". Proceedings of the 19th International Conference on Mining Software Repositories. MSR '22. New York, NY, USA: Association for Computing Machinery. pp. 1–5. doi:10.1145/3524842.3528470. ISBN 978-1-4503-9303-4.
LeetCode questions come with test cases in various programming languages, ... (Python, Java, JavaScript, and C)
- ^ 编程刷题平台 LeetCode 力扣所有题目均已支持华为仓颉语言 [All problems on the programming practice platform LeetCode are now supported in Huawei's Cangjie language]. Sohu. Retrieved 2024-12-03.
- ^ "NeetCode.io". neetcode.io. Retrieved 2023-10-10.
- ^ "Secretary of State". bizfileonline.sos.ca.gov. Retrieved 2024-03-21.
- ^ a b Curry, Rachel (2024-06-24). "AI is shaping the fate of software engineers, but there is a new way to succeed". CNBC. Retrieved 2024-06-26.
- ^ Tang, Winston. "AI cannot replace software engineers—take it from someone who fought to become one and now helps others pursue the career". Fortune. Retrieved 2024-07-31.
- ^ a b Shumin, Liao. "IT Job Interview Prepper LeetCode Pockets USD10 Million From Lightspeed China". www.yicaiglobal.com. Retrieved 2023-08-16.
External links
[edit]LeetCode
View on GrokipediaOverview
Founding and Mission
LeetCode was founded in 2015 by Winston Tang and Hercy Chang, software engineers with experience in the tech industry.[2][9] Based in Silicon Valley, they established the platform to address key challenges encountered in coding interviews.[10] The founders' motivation stemmed from personal experiences navigating technical interviews and the broader need for structured practice in algorithmic problem-solving among software engineers.[11] Recognizing the difficulties in preparing effectively for roles at top tech companies, they aimed to create a dedicated online resource for honing these skills.[12] From its inception, LeetCode's mission has been to empower users to improve their abilities and secure desired positions in the field, particularly through accessible interview preparation tools.[1] This focus on bridging educational gaps in coding practice quickly positioned the platform as a vital tool for aspiring and practicing engineers in a competitive job market.[13]Platform Overview
LeetCode serves as an online judge system that enables users to practice coding problems, offering instant feedback on solutions to simulate real technical interview environments. The platform focuses on algorithmic challenges and data structures, allowing individuals to test their code against hidden test cases for accuracy, efficiency, and correctness. This setup helps users build problem-solving skills essential for software engineering roles.[1] The user base primarily consists of software engineers, computer science students, and job seekers preparing for coding interviews at major technology companies. As of December 2024, LeetCode has approximately 12 million registered users, reflecting its widespread adoption in the tech community, alongside hundreds of thousands of active users participating in daily practice and contests.[14] At its core, LeetCode features a web-based interface that supports multiple programming languages, including C++, Java, Python, C, C#, JavaScript, Ruby, Swift, Go, Scala, Kotlin, and Rust. Users interact through an integrated code editor for writing solutions, a built-in tester for local validation, and a submission system that evaluates code against predefined inputs and outputs. This architecture ensures a seamless experience for iterating on solutions without external tools.[7][15] Accessibility is structured around a free tier that provides basic problem access and core functionality, while a premium subscription unlocks advanced features such as company-specific interview questions, faster code judging during peak times, and exclusive content. The platform is available through its website and is mobile-optimized for on-the-go practice.[16]History
Inception and Early Years
LeetCode was founded in 2015 by software engineers Winston Tang and Hercy Chang as an online platform offering a collection of algorithmic problems focused on data structures and algorithms to help users prepare for technical interviews.[2] The initial launch featured a modest library of problems, with early versions emphasizing practical coding practice in languages like C++, Java, and Python.[17] In its early years, LeetCode operated as a bootstrapped venture, relying on organic adoption within the software engineering community for growth rather than significant external funding.[18] The platform encouraged rapid iterations based on user feedback, with community discussions enabling collaborative problem-solving and content enhancement through shared solutions and insights. This user-driven approach helped refine the experience, as contributors from tech forums provided valuable input on problem quality and platform usability. The founding team was led by Winston Tang and Hercy Chang alongside a small group of international contributors from the US, China, Canada, and India, who handled development and curation in the platform's nascent stages.[2] Growth accelerated through word-of-mouth promotion on sites like Reddit and Hacker News, where engineers shared experiences and recommendations. By 2017, these efforts culminated in a major milestone, with LeetCode surpassing 1 million registered users.[19]Expansion and Milestones
Following its early years, LeetCode experienced rapid expansion from 2018 to 2020, marked by the introduction of weekly and biweekly contests that encouraged competitive problem-solving and community engagement. These contests, featuring four problems of increasing difficulty, became a staple, drawing participants worldwide and fostering a culture of timed practice akin to technical interviews. Concurrently, the premium subscription model, which provided access to exclusive features such as company-tagged problems, mock interviews, and detailed solution explanations, solidified its monetization and supported platform enhancements. This period also saw a surge in international users, particularly during the 2020 remote hiring boom amid the COVID-19 pandemic, as professionals and students globally turned to online resources for interview preparation.[20] Key milestones underscored LeetCode's ascent, including surpassing 2,000 problems in its library by the early 2020s and reaching over 3,000 by 2025, reflecting continuous content curation to cover diverse algorithmic topics.[21] In December 2021, the company secured $10 million in Series A funding led by Lightspeed China Partners, enabling further infrastructure scaling and feature development.[22] The user base continued to expand dramatically thereafter, with over 24 million monthly visits as of October 2025.[8] From 2021 to 2025, LeetCode continued innovating with a mobile-optimized experience launched in 2022, allowing on-the-go practice, though primarily web-based. Team size expanded significantly to 259 employees by 2024, supporting operational growth and global operations.[20] LeetCode's global reach broadened through localization efforts, such as multi-language support for discussions and problem descriptions in select regions, and partnerships with educational institutions via its "Bring LeetCode to Your School" program, offering discounted premium access to groups of 50 or more students to integrate the platform into curricula.[23] These initiatives helped establish LeetCode as a key resource in over 100 countries, promoting equitable access to coding education.Core Features
Problem-Solving Library
The Problem-Solving Library serves as the foundational element of LeetCode, comprising an extensive repository of algorithmic coding challenges aimed at developing users' problem-solving abilities and technical proficiency. As of 2025, it encompasses over 3,000 problems, organized into categories that enable focused practice on specific skills and concepts.[21] Each problem adheres to a consistent structure, featuring a clear textual description outlining the objective, concrete examples of inputs and corresponding outputs to demonstrate requirements, explicit constraints on data ranges and problem scales to inform algorithmic choices, and optional follow-up questions for deeper exploration. Submissions are accepted in numerous programming languages, including Python, Java, C++, C#, JavaScript, and others, evaluated instantly by an automated judge that assesses accuracy, runtime efficiency, and space usage against hidden test cases.[24][25] To support varied practice approaches, the library includes curated collections such as the Blind 75 list, a community-endorsed selection of 75 high-impact problems spanning core data structures and algorithms essential for interview readiness. Premium subscribers gain access to company-specific tags, which filter problems commonly appearing in interviews at firms like Google and Amazon, based on frequency data. Users can also employ built-in tools for random problem selection or topic-based browsing to maintain engagement and variety in their sessions.[26][27] LeetCode maintains the library through regular expansions, incorporating new problems inspired by evolving industry demands in software engineering and competitive programming, often drawn from weekly contests or proactive additions. The platform exclusively owns and provides official editorial explanations, solution code in multiple languages, and comprehensive test case details to facilitate post-submission analysis and learning.[28]Contests and Competitions
LeetCode hosts weekly and biweekly contests, each featuring 3-4 new problems that are subsequently added to the problem-solving library, conducted under timed conditions lasting 90 minutes, with participants ranked on leaderboards based on the number of problems solved and submission times for tie-breakers.[29][30] These contests typically occur every Saturday, allowing global virtual participation without geographical restrictions, and emphasize speed and accuracy in solving algorithmic challenges across diverse topics. Top performers receive prizes such as up to 5,000 LeetCoins, which can be redeemed for platform perks, along with occasional sponsored rewards like merchandise or interview opportunities from partnering companies.[31][32][33] Biweekly contests follow a similar structure but occur every other week, often on alternating Saturdays, with the same 90-minute duration and 4-problem format.[34][29] Prizes mirror those of weekly events, including tiered LeetCoins awards—such as 5,000 for first place, 2,500 for second, and 1,000 for third—alongside items like notebooks or water bottles for higher ranks, promoting consistent engagement among competitive programmers.[31][35] These events serve as a platform for skill-building under pressure, simulating real-world coding interview scenarios while fostering a sense of competition. In addition to standard contests, LeetCode offers other competitive formats including mock interviews for practice, company-sponsored challenges that integrate branded problems with exclusive prizes, and specialized events like university coding competitions.[36][32][37] These vary in structure but often draw from the core problem library, providing targeted experiences for interview preparation or team-based challenges. Participation in contests has grown significantly, with individual events attracting tens of thousands of users—such as over 34,000 in a 2025 weekly contest—and cumulative submissions reaching hundreds of thousands per event across all users.[38] LeetCode employs a ratings system for participants, calculated using an Elo-inspired algorithm that considers expected versus actual rankings, with greater weight on recent performances and provisions for absence forgiveness to maintain rating stability.[39][29] This system, affecting over 400,000 accounts that have competed historically, helps enthusiasts track progress and benchmark skills in competitive programming.[29]Community and Learning Resources
LeetCode's discussion forums serve as a central hub for users to engage in problem-specific conversations, sharing solutions, seeking hints, and clarifying concepts without revealing full spoilers. These forums are organized by individual problems, allowing users to post questions, discuss approaches, and review editorial solutions once attempted. Moderation ensures a spoiler-free environment by flagging or removing content that prematurely discloses answers, fostering a collaborative learning atmosphere.[40] The platform offers curated learning paths designed to guide users through targeted skill development, such as the "Top Interview 150" study plan, which includes 150 classic problems covering key interview topics with high-quality editorial explanations for deeper understanding. Similarly, the "SQL 50" plan focuses on essential SQL queries from basic to intermediate levels, comprising 50 questions ideal for one month of preparation, accompanied by detailed articles on concepts and solutions. These paths integrate briefly with weekly contests by recommending related problems for practice.[41][42] Premium subscribers gain access to advanced resources, including mock interview simulations that replicate real-world pressure by providing timed, company-specific assessments to test problem-solving under constraints. Additional features encompass cloud storage for code snippets and enhanced solution analytics to refine techniques. While AI-powered code feedback and resume reviews are emerging in third-party integrations, LeetCode's core premium emphasizes structured interview preparation tools.[16] To promote consistent practice, LeetCode incorporates user engagement mechanisms like badges awarded for milestones, such as the 50 Days Badge for solving problems over 50 consecutive or cumulative days, and annual badges for extended efforts exceeding 300 days. Streaks track daily submissions, encouraging habitual coding, while progress tracking in user profiles visualizes solved problems, difficulty levels, and topic mastery to motivate ongoing improvement.[43][44]Problem Categories
By Difficulty Levels
LeetCode organizes its extensive problem library into three primary difficulty levels—Easy, Medium, and Hard—to enable users to progress systematically from foundational to advanced coding challenges. This categorization helps beginners build confidence while allowing experienced programmers to tackle complex optimizations, with the overall distribution reflecting a balanced emphasis on skill-building stages. Easy problems emphasize basic programming concepts, such as simple loops, conditional statements, and string operations. These are designed for newcomers to practice core syntax and logic without overwhelming complexity, with classic examples including variants of the "Two Sum" problem, which requires finding pairs in an array that sum to a target value.[45] Medium problems introduce intermediate techniques like basic dynamic programming, binary search, and graph traversals such as BFS or DFS on simple structures. They bridge basic implementation with algorithmic thinking, encouraging users to handle constraints like time and space efficiency in moderately scaled scenarios. Representative examples include problems like "Longest Substring Without Repeating Characters," which applies sliding window concepts to strings.[46] Hard problems demand advanced optimization and deep understanding of data structures, often involving intricate tree or graph manipulations, bit manipulation, or approximations for NP-hard problems like certain scheduling or partitioning tasks. These challenges test the ability to devise efficient solutions under tight constraints, with examples such as "Median of Two Sorted Arrays," requiring logarithmic-time merging.[46] To maximize learning, users are recommended to begin with Easy problems to establish confidence and pattern recognition, gradually advancing to Medium and Hard levels as proficiency grows. This progression mirrors the platform's educational intent, encouraging sustained engagement.[47]By Technical Topics
LeetCode's problem library is structured around technical topics that span core computer science domains, enabling targeted practice in data structures, algorithms, and specialized areas. These tags help users navigate over 3,000 problems as of 2025, focusing on skills commonly tested in technical interviews at tech companies.[48]Data Structures
The platform emphasizes fundamental data structures through dedicated tags, allowing users to explore implementation, manipulation, and optimization techniques. Arrays form a cornerstone, with problems involving indexing, subarrays, and multi-dimensional variants, such as finding the maximum subarray sum or rotating an array. Linked lists cover traversal, reversal, cycle detection, and merging, exemplified by challenges like removing the nth node from the end or detecting cycles using Floyd's algorithm. Stacks and queues address LIFO/FIFO operations, including applications in expression evaluation and task scheduling, while trees and graphs tackle hierarchical and networked data, with binary search trees, traversals (inorder, preorder, postorder), shortest paths, and connected components. Heaps, often via priority queues, focus on extraction, insertion, and k-largest elements, with over 500 problems collectively across these data structures to reinforce conceptual understanding and efficiency.[49][50][51][52][53]Algorithms
Algorithmic tags on LeetCode highlight paradigms for problem-solving efficiency, drawing from classical computer science. Sorting and searching include quicksort, mergesort, binary search on sorted arrays, and interval merging, often requiring O(n log n) or better time complexities. Dynamic programming problems build on overlapping subproblems and optimal substructure, such as the knapsack variant or longest common subsequence, emphasizing memoization and tabulation. Greedy approaches feature selection of local optima, like activity selection or fractional knapsack, while backtracking explores exhaustive search with pruning, as in N-Queens or subset generation. Bit manipulation leverages binary representations for operations like counting set bits or single number finding, providing concise solutions for space-optimized scenarios. These categories encompass hundreds of problems, prioritizing high-impact methods from seminal works like those on divide-and-conquer and recursion.[54][55][56][57][58] Recursion presents particular challenges in advanced problem-solving, particularly among hard problems. The top hard recursion problems, based on lowest acceptance rates from LeetCode's official recursion list, are:- Regular Expression Matching (10) - Hard, 30.3% acceptance rate
- Wildcard Matching (44) - Hard, 31.2% acceptance rate
- Integer to English Words (273) - Hard, 34.8% acceptance rate
- Maximize Number of Nice Divisors (1808) - Hard, 35.2% acceptance rate
- Number of Digit One (233) - Hard, 37.6% acceptance rate
