Learn Coding - Off By One

Land your next tech job. Off By One turns learning to code and coding interview prep into a five-minute daily habit.

Real interview problems, taught the way you actually learn: step by step, with animated visualizations, guided code building, and complexity quizzes. You watch the algorithm move, then you build it yourself, then you prove you understand why it works. No copy-pasting into a judge, no walls of text.

WHAT'S INSIDE • 64 guided lessons across 14 topics: arrays and hashing, two pointers, sliding window, stacks, binary search, linked lists, trees, tries, heaps, backtracking, graphs, dynamic programming, greedy algorithms, and intervals • Every lesson in Python, Java, and JavaScript, each written for that language by hand, never transliterated: the JavaScript version asks JavaScript questions, the Java version asks Java questions • Animated, step-by-step visualizations that show how each algorithm actually works: pointers travel, windows slide, trees traverse • Big-O time and space quizzes on every problem, so you can explain the "why" in the room, not just recite the code • 20 system design stories covering caching, load balancing, sharding, CDNs, rate limiting, database indexing, message queues, CAP, WebSockets, and more • A beginner intro for every topic, so you can start from zero and still end up interview-ready • Streaks, weekly progress charts, and an activity grid that keep you honest, five minutes at a time

HOW A LESSON WORKS

1. Understand the problem and the approach in plain language
2. Watch the algorithm run, one step at a time
3. Build the solution yourself with guided code steps
4. Answer for its time complexity
5. Answer for its space complexity

Finish a lesson and the next one is waiting: the curriculum is ordered so every topic builds on the one before it.

WHO IT'S FOR • Complete beginners who want to learn to code with a clear goal • CS students preparing for internship and new-grad interviews • Self-taught developers filling the data structures and algorithms gap • Working engineers brushing up before the next interview loop

START FREE Every lesson and story opens free: read the problem, watch the first steps, get a feel for it. Premium unlocks full visualizations, code building, complexity training, and system design.

Off By One Premium is an auto-renewing subscription. Plans: annual with a 3-day free trial, monthly with a 3-day free trial, or weekly. Prices are shown in the app in your local currency. Payment is charged to your Apple ID account at purchase confirmation, or when the free trial ends. Subscriptions renew automatically unless cancelled at least 24 hours before the end of the current period. Manage or cancel in your Apple ID settings. Unused trial time is forfeited on purchase.

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