[New Grad] KT DS - Coding Test & Interview (Final Offer) Recap

I applied to kt ds in H2 2021, and my start date was January 10, 2022.

A bit of time has passed, but I'm finally pulling together the KT DS interview / acceptance recap I always meant to write up. (I had some related posts on Naver Blog that I'll be migrating here too.)

💡 Hope this is useful to someone out there.

This post is based on the records I kept through KT DS application all the way to the final interview.

The 2021 hiring timeline:

Here's the recap of the aptitude test, coding test, and interview after passing the document screening.

Figure 1. Document screening — passed

The aptitude test + coding test was scheduled for November 20, 2021 (Saturday).

Notably, even though the role was Application SW Dev/Operations, I had to take both the aptitude test and the coding test.

Platform: Programmers

Time: 3h 30m total including breaks (started 14:00) I connected at 13:30 and was effectively tied to the seat for roughly 4 hours.

Aptitude test (1 hour): Mix of math, language, etc. About 50~60 questions, nothing hard — no prep needed.

Coding test (1 hour): 3 problems — 2 algorithm + 1 SQL. (Difficulty: roughly Silver 4, Silver 1, easy SQL.)

Coding Test Recap (1 hour)

Problem 1 (implementation — Silver 4)

Title: Stock buy or sell (auto problem)

Summary

1. Buy if the price rises 3 times in a row. [5, 3, 4, 6, 7 (BUY), 9, 19, 18, 17, 16, 12, 14, 15, 20, 13]

2. Sell if the price drops 3 times in a row. [5, 3, 4, 6, 7, 9, 19, 18, 17, 16(SELL), 12, 14, 15, 20, 13] (Net profit: 16 - 7 = 9)

3. Continue applying the rules. [5, 3, 4, 6, 7, 9, 19, 18, 17, 16, 12, 14, 15, 20(BUY), 13]

4. Sell unconditionally at the end of Prices. [5, 3, 4, 6, 7, 9, 19, 18, 17, 16, 12, 14, 15, 20, 13(SELL)] (Force-sell on the last element)

5. Compute final net profit and return. [5, 3, 4, 6, 7, 9, 19, 18, 17, 16, 12, 14, 15, 20, 13] 16 - 7 = 9,    13 - 20 = -7 return: 9 - 7 = 2

Problem 2 (implementation — Silver 1)

Figure 2. Problem 2 — hand-drawn reconstruction

I'm sharing my reconstruction for problem 2. (For pacing, I solved 1 and 3 first, then ran out of time on 2 — didn't finish it.)

Problem 3 (SQL — close to Bronze)

Figure 3. Problem 3 — hand-drawn reconstruction

Problem 3 was an SQL problem and came out really easy. Knowing GROUP BY, ORDER BY is enough to solve it.

💡 If you're short on time, just skim through Programmers' SQL problems before going in. (Brush up on JOIN just in case.)

I uploaded my reconstructed solutions to the git repo below. At that time I was using Python, so they're .py files.

CodingTestReproduction/ktds-codingtest · taehyuklee/AlgorithmRepository tracking problems solved on online judges (Baekjoon · Programmers · Softeer · CodeTree).github.com

Pre-Assignment (1 hour)

After passing the coding test, there was a 1-hour window to prepare the PT material for the interview.

Figure 4. Coding test — passed

On November 28, 2021, 14:00 - 15:00, you had 1 hour to work on the pre-assignment. The proctoring platform was Programmers again.

You pick 1 of about 5 topics and use internet search etc. to produce a single-page document based on your own reasoning. The key keywords for the topics: IoT, metaverse, optimization algorithms, etc. — each with concrete scenarios. I can't disclose the specifics due to company confidentiality.

📝 This type of problem likely uses actual scenarios the company is wrestling with.

You build the PPT and submit within 60 minutes — that's it.

Interview

Due to COVID-19, the technical interview (with pre-assignment PT) and executive interview were both held in one day. The interview date was December 2, 2021.

📝 Note: a hiring medical check was scheduled before this, so that came first.

The venue was the Novotel Ambassador Seoul Dongdaemun. After arriving you wait briefly in the sofa area, and interview attendants guide you to the interview floor. Order was technical interview → executive interview.

Before the technical interview, 3 candidates were assigned to one waiting room. I chatted briefly with the candidate next to me to ease the nerves. After a brief wait, the attendant guides you to your interview room.

Right before entering the technical interview room, they hand you a printed copy of the pre-assignment PPT you submitted.

Technical Interview

4 interviewers and 1 candidate — a 4:1 interview. Because of COVID, it ran with a large screen. The interviewers gave a quick (~30 sec) self-introduction, then asked me to present the pre-assignment PT first.

Pre-assignment PT time

I presented based on the topic I picked, with the reasoning I'd worked out. Since I couldn't directly look at the PPT slides during the presentation, I occasionally lost the thread. But I pushed through with my own line of reasoning.

After I finished, the interviewer noted that the question intent I'd captured was slightly off from the actual intent. Then they explained the original intent again and gave me time to think and another chance to respond. I can't share the specific topic, but it was about customer-tailored services.

My takeaway from the pre-assignment PT: there's no single correct answer. As long as you communicate logically with your own reasoning, you're fine. Even if you misread the question intent, don't panic and think "I'm done" — instead, ask the interviewer again and earn another chance. That communication ability matters more. That said, you do need to pick a topic you have at least some grasp of.

Resume-based questions

Just because it's a "technical" interview doesn't mean personality questions are off the table. They drill into your collaboration experience, the languages you can use, your skill set, projects you've done — with follow-up questions. Master your own resume before going in. And rehearse defenses against likely attack angles.

"Do you know what kind of company we are?"

Since I majored in Mechanical Engineering (not CS), they asked me what KT DS does as a company.

💭 At that point, having done AI for machine control in my Master's, I was in a flower-field of "I'll be doing AI modeling" based on the job posting. I didn't even know what SI was.

"For your last words, instead of a closing remark, tell us what you really feel — what you couldn't say."

Reading my writeup, it might sound like I nailed the interview, but the actual interview was basically a muddy brawl. Maybe the interviewer felt how stuck I was and gave me one last chance. Usually you give a closing remark and wrap up — but they gave me a chance to say what I actually felt.

After the technical interview

After the technical interview, the only thought I had was "I'm done." That 30-min muddy brawl feeling still hasn't left me. Maybe because I'd already mentally accepted I was done, I was able to relax — and that's why the executive interview ended up easier.

Executive Interview

The executive interview was a group interview with the 3 candidates waiting together. One person didn't show up, so we ended up as 2 candidates : 5 interviewers.

💭 I'd mentally checked out by then and was rambling, so I barely remember it — but I'll write what questions I can recall.

The executives rotated through the candidates asking the same questions in different orders.

📝 From what other peers told me later, some had a technical interview at the executive stage — I didn't. I mostly got personality questions.

0. Self-introduction

1. MZ-related question — How do you think about the MZ generation?

2. Tell us why we should hire you.

3. If there's an opportunity here to become an executive, are you the kind of person who can become one? → Essentially: tell us why you'd deserve to be promoted to an executive.

That's about all I can remember.

After the executive interview

I was certain: "Yeah, I'm rejected." I didn't feel I'd answered anything cleanly, and the whole thing had been so painful that I figured the interviewers' impression of me was negative.

Before the interviews, they hand out a coffee coupon redeemable at the Novotel 1F café. After everything ended, I had coffee with the candidate I'd shared the executive interview with, shaking off the disappointment. We commiserated, said "hope we see each other again — at a better place next time", and parted on a warm note.

Believing I'd been rejected and just plowing through my Master's thesis and journal paper, on December 22, 2021, the final result dropped.

Figure 5. Final result — accepted

I doubted my eyes. The news "you've passed the final round" hit me as "Wait?? Me??".

But after getting dropped by SK E&S, Samsung Electronics, SKCT, Samsung coding test, etc. and my confidence steadily eroding, this was an enormous relief. I submitted the final acceptance documents with great joy and joined kt ds.

Wrap-up

Honestly, at the moment I joined kt ds, I didn't even know what SI meant, what kind of IT work happens day-to-day, or technically what an API was. I had depth in mechanical-engineering-domain AI from a math/stats angle, but almost no exposure to IT specifically — so once inside, I went through hell, studying on my own day and night.