computer science

LeetCode

LeetCode is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand LeetCode rather than just read about it. In short: LeetCode is an online platform for software coding interview preparation. The site provides algorithmic problems intended for users to learn and practice programming.

Key takeaways

LeetCode belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect LeetCode to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of LeetCode from memory before moving on to harder problems.

Reference excerpt

LeetCode is an online platform for software coding interview preparation. The site provides algorithmic problems intended for users to learn and practice programming. Since the company founding in 2015, the LeetCode platform has gained popularity among job seekers in the software industry and coding enthusiasts as a resource for technical interviews and coding competitions. As of 2025, the website has 26.3 million monthly visitors.

History LeetCode was founded in Silicon Valley in 2015 by Winston Tang. After moving to the US from Malaysia in 2005, Tang founded the company, citing his own experiences working at Amazon and Google as inspiration. LeetCode expanded its operations to China in 2018, providing Chinese problems, solutions and forums on its Chinese website Likou (Chinese: 力扣; pinyin: Lìkòu). In 2021, LeetCode secured its first round of funding, receiving a $10 million investment from Lightspeed China Partners.

Features 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. The performance of users' solutions is evaluated based on execution speed and memory usage, and is ranked against other submissions in the LeetCode database. Additionally, LeetCode provides its users with mock interviews and online assessments. LeetCode hosts weekly and biweekly contests, each having 4 problems. After participating in a contest for the first time, one gets assigned a ranking, which can be found in their profile. 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. LeetCode supports a wide range of programming languages, including Java, Python, JavaScript, and C. Since September 2024, LeetCode China supports Huawei's Cangjie programming language for all problems. The platform features forums where users can engage in discussions related to problems, the interview process, and share their interview experiences.

Types of problems 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. As of January 2026, LeetCode offers 3816 questions across its three levels of difficulty; with 922 questions categorized as easy, 1922 as medium, and 902 as hard.

See also Coding interview Competitive programming Advent of Code Codeforces HackerRank

References

External links Official website

Worked examples

Example 1 — a first encounter with LeetCode

Start with the simplest possible case. Write down what LeetCode claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to LeetCode before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about LeetCode ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of LeetCode

In research: LeetCode appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses LeetCode in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: LeetCode is common in secondary-school and first-year university syllabi. It links to neighbouring topics American educational websites, Computer science competitions, Programming contests, so understanding it makes those chapters shorter.
In everyday life: Look for LeetCode outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study LeetCode in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what LeetCode means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain LeetCode out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is LeetCode in simple terms?

LeetCode is an online platform for software coding interview preparation. The site provides algorithmic problems intended for users to learn and practice programming.

Why does LeetCode matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study LeetCode?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on LeetCode.