Russell Saerang

30 September 2026 • 6 minutes read

I was at a house party spectating my friends solving math problems for fun when we stumbled across this high school olympiad question: Given $n$ numbers $a_1 \ge 1$ and $a_{i+1} \ge a_i+1$ for $1...

31 August 2026 • 9 minutes read

Sorry that I had to write this closer to the end of the month! I have been busy grinding Kattis and my actual irl work stuff, but the storm is starting to settle down and I can finally sit down and...

1 July 2026 • 10 minutes read

Following my "hiccup" in CAT2026's preliminary round batch 2 while solving problem D, I've come to realize that my Python dynamic segment tree was still very suboptimal. Understandably, the...

14 June 2026 • 22 minutes read

Coding and Algorithms Tournament 2026 has finally come to a wonderful conclusion! Congratulations to all the winners, and good job to the organizing committee for pioneering such a well-executed...

10 May 2026 • 18 minutes read

Because... Japan. First time going with my parents after almost 24 years of living in this silly world, so I thought I'd document this in case future first-timers might need it. The trip started by...

1 April 2026 • 2 minutes read

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2 March 2026 • 18 minutes read

Integer factorization is one of the most useful techniques in competitive programming when it comes to handling large numbers. Once we know the list of the prime numbers $p_1, p_2, \ldots, p_k$...

1 February 2026 • 9 minutes read

Let's just say this is an old habit that dies hard and therefore worth another write-up. As of the moment of writing, NUS CS1010A (then CS1010S) practical exams always come in 4 questions of the...

1 January 2026 • 18 minutes read

Happy new year, everyone! I'm kicking off the year by sticking to my monthly writing goal in this website. I think it's a good way of documenting the interesting things I encountered during my...

12 December 2025 • 40 minutes read

I have been doing Advent of Code (AOC) since 2021 and have completed all questions from 2015 as of writing this article. While the initial goal was to learn new languages (like Haskell and Rust), I...

2 December 2025 • 30 minutes read

It all started back in 2021 when I saw this problem on Kattis that asks you to multiply two polynomials. Given the constraints, directly multiplying them (like how people would in mathematics...

3 November 2025 • 27 minutes read

This article serves as a detailed breakdown of the code provided in pytils. The degree sequence of a graph is defined as a non-increasing sequence of the graph's vertex degrees, where the degree of...

30 September 2025 • 17 minutes read

It's been a month since the second season of Clash of Champions' final episode. While the games were entertaining and the questions were interesting to try out along, I decided to take things up a...

6 August 2025 • 7 minutes read

It was the COVID era where everything was online, thus the rise of Telegram scammers trying to add random users to a particular set of scam and/or spam investment group chats. It was very...

1 July 2025 • 9 minutes read

Having done several competitive programming (CP) problems in pure Python, it is safe to say that recursion is worse for most instances, especially for problems with tight memory or time limit....

4 September 2024 • 11 minutes read

Since I am no longer teaching CS2040 (Data Structures and Algorithms) as an undergraduate teaching assistant in NUS, I thought it would be nice to dump some additional Kattis problems here...

28 July 2024 • 7 minutes read

Let's start with an array $A$ of size $N$, each entry is initially zero. Suppose that over time, I want to support these operations on the array: We can do this naively with a single for loop,...

22 July 2024 • 5 minutes read

Suppose you have a set $S$ of $N$ different objects, each object having different scores for a particular set of metrics. Suppose we ask ourselves this question: How does one select as many objects...

28 February 2024 • 3 minutes read

Let us start off with a simple triangle $\triangle ABC$. We draw the altitudes for each respective vertex, intersecting the corresponding sides at $H_A, H_B, H_C$. It is a well-known fact that...

14 January 2024 • 10 minutes read

The original article was written in 23 June 2020 and was written mainly based on my own opinion. I will mainly discuss about NUS and NTU scholarships interviews. Other universities' may go the same...