Fenwick Trees are often introduced as a compact implementation trick for prefix sums.

But the interesting part is not the code. The interesting part is the binary structure underneath:

why ranges partition the way they do what i & -i is actually extracting how prefix traversal emerges naturally from binary decomposition why both updates and queries become logarithmic

I made a video trying to build intuition for these ideas visually and structurally rather than treating BIT as something to memorize.

Topics covered:

• naive approaches and prefix sums
• lowest set bit (LSB)
• derivation of i & -i
• block size interpretation
• traversal logic
• implementation walkthrough

Video: YouTube link Would genuinely appreciate feedback from experienced CP users on the content, and from people learning if its easier to understand especially if there are cleaner ways to think about or explain the structure.

References:

• A New Data Structure for Cumulative Frequency Tables: https://blogs.asarkar.com/assets/docs/algo...

• Fenwick Tree (Competitive Programming): https://cp-algorithms.com/data_structures/...

• A question to test out your knowledge: https://mirror.codeforces.com/contest/2227/problem/G

AMS Derive 2026 — An Invitation to Problem Setters

AMS (Algorithms & Mathematics Society) is building the problem set for AMS Derive 2026, a three-round quantitative contest circuit. This is a direct invitation to mathematicians and quant thinkers who set problems at a research level.

What AMS Derive is

No standard DSA template is applicable to any problem in this set. Every solution requires constructing a mathematical framework from scratch. Our opening round had 600+ registrants across IITs, IISc, BITS, and other top university. One problem had 6 correct solutions in the entire field.

What we are looking for

Problems in any of the following domains:

• Stochastic Processes
• Probability Theory and Bayesian Inference
• Market Microstructure
• Options Pricing Theory
• Combinatorics under probabilistic constraints

The bar is high. Problems must be novel, mathematically rigorous, and impossible to solve by pattern recognition alone. If you have solved 2000 Codeforces problems, that background alone will not help you here. If you understand measure theory, martingales, or microstructure, this invitation is for you.

What accepted problem setters receive

Full credit on the AMS Derive problem set. The editorial and complete problem set are published publicly after each round and reviewed by quant firm representatives on the evaluation panel, direct visibility with the people who hire for quantitative research roles in India.

Accepted contributors share a $1000 USD pool distributed across the three rounds, weighted by accepted problems.

Express interest: Submit your interest here

Questions: admin@amsociety.in

Hello Codeforces!

We are delighted to invite you to participate in AMS Round 1! The contest will take place today, 1st of March, 2026 at 2:00 PM IST. (~1 hour)

All participants with any ratings are, of course, warmly welcomed to participate in the competition. You will be given 6 problems and 2 hours to solve them. The round will be held under standard Codeforces rules.

Link: https://mirror.codeforces.com/contestInvitation/21752a9c2925f7bd557a64bce654343fd4f6b9fc

This round is the debut of the AMS team! We have poured a lot of love and effort into creating problems that we hope you will find mathematically beautiful, probabilistically interesting, and educational.

Prizes & Sponsorship: We are thrilled to partner with getcracked.io for our debut round. Because they are dedicated to elevating algorithmic problem-solving and rigorous interview prep, their platform is a highly valuable resource for this community. By climbing the leaderboard, you can win premium access to their tools:

Top 3 Rank-holders will get 3 months of membership at getcracked.io Rank 4 — Rank 10 will get 1 month of membership at getcracked.io Registration Details: The registration portal will be available exactly 6 hours before the contest begins. Registration Opens: 8:00 AM IST, Sunday

Platform: A huge thank you to MikeMirzayanov for the amazing Codeforces and Polygon platforms!

A Final Note We highly recommend reading all the problems, as the difficulty might be subjective. We hope you enjoy the problems as much as we enjoyed creating them.

Good luck, have fun, and see you on the leaderboard!

Hello Codeforces!

We are delighted to invite you to participate in AMS Round 1! The contest will take place tomorrow, 1st of March, 2026 at 2:00 PM IST.

All participants with any ratings are, of course, warmly welcomed to participate in the competition. You will be given 6 problems and 2 hours to solve them. The round will be held under standard Codeforces rules.

This round is the debut of the AMS team! We have poured a lot of love and effort into creating problems that we hope you will find mathematically beautiful, probabilistically interesting, and educational.

Prizes & Sponsorship: We are thrilled to partner with getcracked.io for our debut round. Because they are dedicated to elevating algorithmic problem-solving and rigorous interview prep, their platform is a highly valuable resource for this community. By climbing the leaderboard, you can win premium access to their tools:

• Top 3 Rank-holders will get 3 months of membership at getcracked.io
• Rank 4 — Rank 10 will get 1 month of membership at getcracked.io

Registration Details: The registration portal will be available exactly 6 hours before the contest begins. Registration Opens: 8:00 AM IST, Sunday

Platform: A huge thank you to MikeMirzayanov for the amazing Codeforces and Polygon platforms!

A Final Note We highly recommend reading all the problems, as the difficulty might be subjective. We hope you enjoy the problems as much as we enjoyed creating them.

Good luck, have fun, and see you on the leaderboard!

At the Algorithms & Mathematics Society (AMS), we explore the space where deep algorithmic thinking meets quantitative finance. To gear up for our upcoming AMS Official Round 1 (1st of March, 2026), we’ve just dropped a practice teaser problem: the Option Payoff Calculator.

The Teaser Challenge (A — level): If you're interested in the math behind the markets, this one is for you. You're tasked with evaluating a simple call option on a stock. Given a strike price, current price, and a set of possible future price levels with their respective probabilities, can you calculate the expected payoff of the option?

It's a perfect blend of expected value mathematics and implementation logic. It might sound straightforward, but structuring your logic to handle the inputs efficiently and computing the exact floating-point output is key.

Why This Matters This problem is a classic example of applying probability to derivative pricing—a basic fundamental concept for anyone looking to build a strong foundation in Quant finance and high-frequency trading. It's exactly the kind of practical, market-driven logic we love to test.

Ready to Code? Write your solution: C++, Python, Java, Go—use whatever language you're most comfortable with. Submit: Email your source code to admin@amsociety.in with the subject line "AMS Round 1 Teaser [Your Name]".

This is a practice run to get you warmed up, so it won't affect your AMS contest rating. The official solution and editorial will be released on Sunday, February 22nd.

AMS Round 1 Link: https://mirror.codeforces.com/contestInvitation/b03d1231743513f093a32dda767b04cb3fd1bcda

AMS Website: www.amsociety.in Let's see what you've got. Happy coding!