Why does this exist?

Imagine your toys are scattered all over your room. Data Structures are the different types of toy boxes you use to organize them — a bin for blocks, a shelf for books, a hook for backpacks. Algorithms are the steps you follow to do something with the toys — like "how do I find my favorite car the fastest?" or "how do I line up my stuffed animals from smallest to biggest?"

Every data structure is just: a box + rules for how you're allowed to put things in and take things out. Every algorithm is just: a recipe — a list of steps that always gets you the right answer.

That's it. Everything below is that idea, over and over, in fancier clothes.

We'll go Beginner → Intermediate → Advanced. Every topic has:

• 🧸 ELI5 — the toy-box explanation
• 🌍 Real life — where you already use this without knowing it
• 📝 Pseudocode — the recipe in plain steps
• 🐹 Go code — the real thing, with the standard library doing the heavy lifting
• 🇨 C code — the same structure with no standard library to hide behind: you write the malloc, the pointer chasing, and the array-index math yourself
• ⏱️ Complexity — how the recipe scales when you have way more toys

Why both languages? Go's map, container/heap, and garbage collector do real work you don't see. Writing the same data structure in C forces every piece of that work into view — which is exactly why this guide's C examples are paired with wiki/c-lang/real-life-c-guide.md, a full C field guide: its Part III ("Data structures from scratch," §17–19) builds the linked lists, hash tables, and trees used below in more depth, and its Part VIII covers the memory-safety discipline (leak patterns, ownership rules) every one of this guide's malloc/free pairs relies on. Each 🇨 block below links to the exact section that goes deeper.