# [CS Technical Interview 5] Data Structures That Click

🥲 Getting a developer job - coding tests weren't the end of it.

As a non-major, when I first prepared for a developer job, I was obsessed only with algorithms and coding tests. I gained some confidence and passed most coding tests. However, I kept failing at technical interviews, the next hurdle.
What was the problem? It was the lack of CS (Computer Science) knowledge. In interviews, CS fundamentals were considered much more important than algorithms.

🗣 In real interviews, 'speaking practice' was important.

Even after filling in my CS fundamentals, interviews were not easy. At a certain company's interview, I was asked about floating-point numbers. It was content I had definitely read and thought I understood multiple times in books, but I couldn't utter a single word. That's when I realized it. Passive learning through simply reading and understanding cannot help you answer in real situations.

To succeed in interviews, you need not only to accumulate a lot of knowledge but also the ability to explain that knowledge. This 'ability to explain' can only be developed through practicing organizing concepts into just a few sentences and articulating them out loud. Through this process, you can also discover what you didn't understand precisely. Without this practice, you'll encounter the following problems.

1. Concept Confusion Type

❓InterviewerWhat are the characteristics of object-oriented programming?
💬 Candidate The SOLID principles. First, S stands for..(omitted)...

This is a case of confusing similar concepts.
SOLID is an OOP design principle, and the characteristics of object-oriented programming are abstraction, encapsulation, inheritance, and polymorphism.
The moment you mix up related concepts, the interviewer judges that 'your fundamentals are shaky.'
It's not just a simple mistake, but rather it's read as a signal that the conceptual framework isn't solidly established.

2. Lack of Specificity Type

❓Interviewer What are the characteristics of TCP?
💬 Candidate It's a protocol that guarantees reliability.
❓ Interviewer What mechanisms guarantee reliability?
💬 Candidate Um... well... it ensures safe transmission... like...

This is a case where you only know the What, but lack the How/Why.
You only know the superficial answer and aren't prepared to explain the underlying principles.
Communication is agreed upon through TCP connection (3-way handshake), reliability is guaranteed through RDT (sequence numbers, ACK, retransmission, etc.), and quality is maintained through flow control and congestion control.
These concepts need to be connected as a single flow in your mind. If you haven't organized the concepts concretely, you won't be able to handle follow-up questions.

3. Getting Stuck on Basic Questions

❓Interviewer What is HTTP?
💬 Candidate Um... it's for sending and receiving data on the web... something like that...?

It's such a familiar concept, yet when asked to explain it in one sentence, the words don't come easily.
Terms like request, response, server, and client come to mind, but they don't flow naturally into a coherent sentence.
This is because we've never practiced explaining from definition to principle in one continuous flow.
This isn't a lack of knowledge—it's an absence of structure.

Knowing alone is not enough. It becomes true skill only when you can explain it in words.

🔥 So I created it. The CS Technical Interview Series That Makes You Fluent!

🎯 Recommended for

Non-majors · Job seekers · Career changers and others preparing for technical interviews who need to be able to articulate CS fundamentals verbally

⚡ Course Essentials Kick

📘 Technical Interview Practice WorkbookProvided

💡 Use it like this

💬 Q. The lecture time is short - will I be able to learn properly?

🖐 Hello! Let me introduce myself! 🙇

I created this course remembering my past self, who stayed up all night worrying about the fundamentals and felt anxious over a single interview question.

I started as a non-CS major and understand better than anyone the thirst for fundamentals (CS knowledge, programming languages, etc.). After diving into countless materials through self-study and building my own know-how, I eventually graduated from Seoul National University and now work as a 🧑🏻‍💻 Kakao developer.

From a young age, I was more confident than anyone in combining and reconstructing various materials to create 'my own consolidated notes.' This course is a secret notebook born from that 'ultimate self-study know-how' and all my passion and philosophy.

🔥 What makes this course special?

• All of my 'know-how' is contained here: As a non-major, I've fully incorporated my experience and know-how of self-studying CS and programming languages and getting hired at a large corporation. This course contains all the methods for how to most efficiently understand complex and abstract concepts and make them your own.

• 'Fundamentals' are key in any development field: Whether you're pursuing game development, AI, web/app development, or any other field, foundational knowledge in computer science is not optional—it's essential. This course helps you become a true expert by building a solid foundation.

• 'We compete with overwhelming quality': I've extracted key concepts by referencing numerous materials including textbooks, lectures from prestigious universities, commercial books, and technical interview resources, then reconstructed them in my own unique way. With intuitive diagrams and illustrations, combined with easy-to-understand explanations infused with my practical experience, I promise to make even complex concepts click with an "Ah, now I get it!" moment.

🚀 Introducing the fifth lecture [Data Structures] from the Technical Interview Master Roadmap.

📕 Data Structures: Develop Your Intuition for 'When to Use What!'

Data structures go beyond simply knowing the concepts,

• Still confused about when to use stacks and queues❓

• Are you struggling to understand how complex data structures like trees and graphs are applied to real-world problems❓

In other words, it's a subject where you need to develop an intuition for "when and which structure is best to use?" However, for beginners, various structures are scattered in fragments, and it often leads to frustration because they can't grasp where and how stacks/queues/trees/graphs are used.

This course is designed specifically for such individuals, delivering the core concepts of each data structure intuitively through diagram-centered visualization, and clearly comparing the pros and cons and selection criteria for each structure so you can easily understand and remember them for a long time. I strongly recommend this course to those who have done basic coding but found data structures overwhelming, and those who want to organize their CS theory knowledge.

🎯 Through this course, you will be able to answer the following questions clearly.

How do arrays and linked lists differ in structure, and what situations is each suitable for?
→ Explains the core concepts visually, focusing on the differences in memory layout, access methods, and insertion/deletion operations.

How do stacks and queues process data according to their rules?
→ We organize the LIFO and FIFO principles with diagrams and examples, and also convey their practical application contexts.

What are the structural differences between trees and graphs?
→ We've organized the content to help you clearly understand and distinguish essential concepts such as hierarchical structure, presence of cycles, and traversal methods.

When is a heap useful?
→ Through priority queues and the principles and implementation methods of min/max heaps, we systematically explain how heaps work.
→ We also cover practical use cases such as sorting and scheduling.

📌 At the end of the course, a practical interview practice chapter awaits you.

"What is the difference between arrays and lists?", "What are the conditions for a good hash function?",
"What is a heap data structure?" - you can
practice organizing and articulating answers to frequently asked technical interview questions like these.

📖 A curriculum packed with essentials

This is the table of contents and key keywords you will learn in this course.

If there are any unfamiliar keywords, make sure to grasp them firmly this time.

✏ Here's what you'll learn

👀 Course Preview

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💡 Looking for other interview preparation courses? Check out the roadmap below :)

🔗 Technical Interview Master Roadmap

Notes Before Taking the Course