Small introduction for new 200 people.

So, I'm Andrii, next month will be 8 years since I started making money out of software engineering.

I'm originally from Ukraine and started my path as a Junior .NET developer at a small outsource company in 2018. I was very lucky and got an extremely good techlead that suggested me a bunch of books and direction for development. Since then every year (and a half) I was switching these outsource companies on the next level (fake levels). In 2020 got a fake Senior offer from Epam, and since then decided to try big tech.

Failed my first interview for AWS, but succeeded Microsoft's one, and relocated to Prague. At MS I got a pretty bad project initially (Dynamics 365) and after one year passed the interview to Teams' Presence service (green/yellow/red indicator of your status: in a meeting, in a call, etc.). It was the best project in my whole life so far, high load (over 1M req/s), custom replication, custom sharding, global rollout with the best practices, etc.

But I got a bad visa (temporary protection) therefore decided to pursue another opportunity in an English-speaking country, since a Senior promotion at MS wouldn't matter moneywise that much for me, and on-hire stocks were almost over.
Prepped for 3 months, and landed Snowflake and Google offers, but decided to move forward with Snowflake.

And here we are, already half a year I'm here in Dublin, let's see how it goes.

I guess you have already checked the content. Main focus is on Leetcode as it is still widely asked in interviews, and I'm paranoid about layoffs. Besides that I'm doing System Design that I'm genuinely enjoying. As part time I'm helping people to prep for big tech companies and doing mock interviews. Apart from it, sometimes I'm doing some small articles/content about work-related stuff: PG race conditions, TLS deep dives, OAuth deep dives, etc. Some time ago I was also streaming the Leetcode/System design, but not anymore. I will start once I'm prepping for Google next time.
From time to time you might see some misc content related to music or boxing, as this is what I do when I'm not busy with programming.

I love pets, and there is Mr Orange that I am feeding daily. You are gonna see him frequently.

Daily (302/373 streak until LC cap)

Pretty simple one tbh, I was even not sure my approach is the right one (check thecomments)

https://leetcode.com/problems/create-binary-tree-from-descriptions/description/?envType=daily-question&envId=2026-06-07

#daily #medium #nopattern

Cooking, want to give a bit of math background.

Yes, turns out, for the Nth time, math is needed if you are doing something more complicated than crud on backend

Daily (303/373 streak until LC cap)

Pretty simple for O(n) space complexity, for O(1) - not sure possible (as quicksort would give absolute order). But nice problem overall.

https://leetcode.com/problems/partition-array-according-to-given-pivot/description/?envType=daily-question&envId=2026-06-08

#daily #medium #nopattern

Was working on it whole day today. Tomorrow Im dropping it here (if oncall is not bad for me).

Daily (304/373 streak until LC cap)

The problem is much much easier than you think. It has a lot of unnecessary details that are irrelevant.

https://leetcode.com/problems/maximum-total-subarray-value-i/description/?envType=daily-question&envId=2026-06-09

#daily #medium #nopattern

Promised - done. This is pretty much polished personal notes that I have gathered over the time. Hopefully will be useful at least for somebody

https://andreyka26.com/ssl-tls-mtls-for-system-design-in-simple-words

Will appreciate feedback/comments.

Overall article creation takes around 12-14 hours usually, which is surprisingly long to me, but it has ZERO AI, everything is written by me, only grammar (missed the/a) is done by AI.

Therefore it might have some mistakes, slightly off information - so let me know, I will update, and mention you in the article as reviewer (always grateful for deep technical review).
BTW this is applied to all my articles, I'm missing review same way as I would miss PR review when doing something myself.

Overtimes, ofc

We both had dinner, now time to sleep

Daily (305/373 streak until LC cap)

As was forecasted yesterday: it is segment tree, and it is hard one.
But with hints + and our segment tree pattern it is not hard to solve.

https://leetcode.com/problems/maximum-total-subarray-value-ii/description/?envType=daily-question&envId=2026-06-10

#daily #hard #pattern

Again, recall this pattern, after doing that I was able to write min/max segment tree in one go.

Putting a reminder: I have a friend who got asked segment tree question in big tech. So it is getting asked.

Btw, this is not company related thing, I drew it, it is kernel network hooks. You all have it on your machine and on your servers