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Visual guides for complex technical topics — DSA, system design, security, cloud, AI, and beyond. Learn through interactive animations and flowcharts.

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Interview concepts in under a minute, animated.

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Latest Articles

In-depth reads on AI, systems, and engineering concepts.

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dsa

Time and Space Complexity — The Scale Lens

Dungeon 0. Before you fight any boss, learn to read the O(n) runes. A complete, interview-ready guide to time and space complexity: how to analyze any code, say the answer out loud and then make it faster.

Rotate Image — The Mural Turn

Dungeon 18, Boss 1. A museum's square mosaic mural must make a quarter turn clockwise, but the tiles are mortared to a frame that cannot move, and no second frame exists. All you can do is swap tiles in place. Mirror the mural across its diagonal, then flip each row, and two reflections quietly add up to one rotation.

Spiral Matrix — The Spiral Plow

Dungeon 18, Boss 2. A farmer plows a rectangular field in a spiral, never crossing a furrow he's already cut, and you have to write down the order the soil turns. Four boundary fences that shrink inward do the whole job, but skip one mid-loop check and a single-row field gets plowed twice.

Set Matrix Zeroes — The Condemned Rows

Dungeon 18, Boss 3. A building inspector walks a grid of storage units where one structural failure condemns an entire corridor and an entire stack. No notebook allowed, so every marking has to go on the units themselves. The matrix's own first row and column become the clipboard, and the order you erase them decides everything.

Happy Number — The Numerologist's Loop

Dungeon 18, Boss 4. A carnival numerologist runs your lucky number through a ritual: square each digit, add them up, repeat. Some numbers ascend to 1 and are declared happy. Others circle the same values forever. Spot the trap without waiting forever, using a cycle detector you already own from the linked list dungeon.

Plus One — The Odometer Tick

Dungeon 18, Boss 5. An old mechanical odometer needs one more mile ticked onto it. Most miles just bump the last wheel, but a wheel at 9 rolls to 0 and nudges its neighbor, and a full row of 9s needs a brand new wheel bolted on the front. Walk the digits backward, return early, and meet carry propagation in base 10.

Pow(x, n) — The Paper Fold

Dungeon 18, Boss 6. A paper craftsman has to build a stack that doubles in thickness a billion times, and gluing one layer at a time would outlive him. Then he folds the strip once and everything changes: one fold doubles the whole stack. Computing x to a huge power works the same way — square what you have instead of multiplying one at a time, and two billion steps collapse into thirty-one.

Multiply Strings — The Abacus Clerk

Dungeon 18, Boss 7. Two cargo values arrive at the customs house so large they overflow every register in the office, and the clerk multiplies them anyway, bead by bead on an abacus. School long multiplication was secretly an addressing scheme all along: digit i times digit j always lands in cells i+j and i+j+1. Allocate m+n cells, pile up the raw products, sweep the carries once.

9 min

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Latest Guides

Click any card to explore an interactive guide.

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Programming

Elo Rating System

Learn how the Elo rating system turns wins and losses into skill ratings — expected scores, K-factors, zero-sum updates, and why beating a stronger player pays more.

Understand how Bloom Filters use hash functions and bit arrays to answer membership queries with zero false negatives, perfect for space-constrained systems.

Client-Server Architecture

Client-Server Architecture is the foundational model of modern networked applications — clients send requests, servers process and respond. Understanding this model is the first step to mastering distributed systems, APIs, and scalable web applications.

A comprehensive guide to Forward Proxy and Reverse Proxy, their differences, use cases, and how they protect clients and servers.

Microservices Architecture

Breaking down monolithic applications into small, independent, loosely-coupled services.

Monolithic Architecture

A single-unit software architecture where all components are tightly coupled.

Serverless Architecture

Serverless architecture allows building and running applications without managing infrastructure.

Big O Notation & Complexity

Understand Time and Space Complexity, Big O Notation, and visualize how algorithm performance scales with input size in worst-case scenarios.

by Obydul

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Series

Follow structured learning paths from start to finish.

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1 / 1 articles

Foundations

Dungeon 0. The training grounds before the first boss. Learn to read the O(n) runes on every boss card: time complexity, space complexity and how to spot a faster weapon in any code you see.

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5 / 5 articles

Applied ML Systems

Real ML systems that companies hire for — fraud detection, credit scoring, recommenders, and forecasting. The problems fintech and government AI teams solve every day, plus how to reason about them in system design interviews.

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10 / 10 articles

Classical Machine Learning

The models that run most production ML today — regression, trees, gradient boosting, clustering, and how to evaluate them honestly. What fintech and enterprise ML teams actually ship.

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7 / 7 articles

Statistics & Probability

The language of uncertainty that every ML model speaks — probability, distributions, Bayes, hypothesis testing, and the bias-variance tradeoff. The screening layer of every ML engineer interview.

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14 / 14 articles

Python Fundamentals

Master Python basics the way you grind LeetCode: by practicing, not re-reading. Learn each concept first from a resource like learnpython.org, then come back here and drill chapter-wise — predict outputs, spot gotchas, and explain the why out loud. Chapters 1 to 10 cover the core language; 11 to 14 are the typing, decorators, testing, and async depth that senior interviews actually probe.

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12 / 12 articles

Essence of Calculus

A geometric, intuition-first walk through calculus, inspired by 3Blue1Brown's classic series. Each chapter builds the picture before the formula: what a derivative really measures, why the chain rule looks the way it does, and how integration undoes it all. Chapters 1 to 4 are the gradient-and-chain-rule core that backprop is built on. Every article links the original video.

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16 / 16 articles

Essence of Linear Algebra

A geometric, intuition-first walk through linear algebra, inspired by 3Blue1Brown's classic series. Each chapter builds a mental picture first, then the math. Chapters 1 to 3 are the fundamentals everything else stands on. Every article links the original video.

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6 / 6 articles

Advanced Graphs

Dungeon 15. Dijkstra, Bellman-Ford, Prim's MST, Eulerian paths, topological sort. The algorithms that power routing, scheduling, and infrastructure.

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