DSA Foundations

Data structures and algorithms from zero — no computer science degree assumed. Plain language, real-world analogies, and the exact patterns interviewers actually test.

0 of 30 lessons complete~318 min total

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What an Algorithm Actually IsAn algorithm is a set of steps for getting something done — like a recipe. By the end of this lesson, the word will stop sounding scary.9 min
Big O, in Plain LanguageBig O is just a way of describing how much MORE work a task takes as the input gets bigger. No formulas required to get the idea.12 min
Trading Memory for SpeedSometimes you can make code faster by having it remember answers it already worked out. That trade — memory for speed — is one of the most useful ideas in this whole track.10 min
Recognizing Big O by EyeYou don't need to calculate Big O with math. You can recognize the four most common patterns — O(1), O(n), O(n^2), O(log n) — just by looking at the shape of the code.13 min
What an Array Actually Is in MemoryAn array is a row of numbered boxes sitting side by side in memory. That single picture explains why reading is instant but inserting in the middle is slow.11 min
Strings Are Arrays of Characters UnderneathA string is a row of characters sitting side by side, just like the array of boxes from the last lesson. That's why some string operations are slow, and why JavaScript strings can't be changed in place.10 min
Hash Maps: The Instant Lookup TrickWhy looking something up by name or key feels instant, no matter how many things you're looking through — the same trick behind a coat check ticket.10 min
Sets and UniquenessA collection that automatically refuses duplicates — useful anytime the real question is 'have I seen this before,' not 'how many times.'8 min
Stacks: Last In, First OutWhy undo history and the browser back button both work the same way — the last thing you did is the first thing that gets undone.9 min
Queues: First In, First OutThe checkout-line rule, turned into code: whoever got in line first gets served first.8 min
Recursion: A Function That Calls ItselfIf the word 'recursion' makes you tense up, that's a completely normal first reaction — here's the idea, stripped down to something small enough to actually follow.12 min
The Recursion Leap of FaithThe single habit that unblocks recursion for most people: trust that the smaller call already works, instead of tracing every call by hand.12 min