the index
All 44 topics
Already know what you're after? Search it, or scan the whole curriculum below, and jump straight in — no need to walk the roadmap.
Foundations
5- FoundationsArrays & MemoryThe row of numbered boxes that everything else is built on.8m 50 XP
- FoundationsStringsA string is an array of characters. Everything else follows from that.8m 55 XP
- Foundations2D ArraysThe grid is a fiction. Memory is one flat line — and that's why row-major is fast.9m 60 XP
- FoundationsHash MapTurn a key straight into a location — the structure behind almost everything.11m 85 XP
- FoundationsSetsA hash map that threw away the values — and answers 'seen this before?' instantly.7m 55 XP
Searching
3Sorting
9- SortingBubble SortCompare neighbours, swap if they're wrong. Repeat until calm.8m 50 XP
- SortingSelection SortFind the smallest. Put it in front. Repeat.7m 50 XP
- SortingInsertion SortHow you actually sort a hand of cards, without being taught.8m 55 XP
- SortingMerge SortSplit until it's trivial, then merge back in order.12m 90 XP
- SortingQuick SortPick a pivot, split around it, and let the halves sort themselves.11m 90 XP
- SortingHeap SortTurn the array into a heap, then keep taking the biggest off the top.11m 90 XP
- SortingShell SortInsertion sort, but values are allowed to leap instead of crawl.9m 75 XP
- SortingCounting SortSorts without comparing anything — and that's how it beats n log n.9m 75 XP
- SortingRadix SortSort by the last digit first. It sounds backwards, and it's the only way it works.10m 85 XP
Linear structures
4- Linear structuresStackLast in, first out. The undo button of data structures.7m 50 XP
- Linear structuresQueueFirst in, first out. Fairness, as a data structure.7m 50 XP
- Linear structuresDequeA queue open at both ends — a stack and a queue in one structure.8m 60 XP
- Linear structuresCircular QueueA queue in a fixed array that never shuffles — the pointers go round instead.9m 70 XP
Linked structures
3- Linear structuresLinked ListNo shelves, no addresses — just a chain of notes saying 'next'.11m 75 XP
- Linked structuresDoubly Linked ListOne extra pointer per node — and the singly linked list's worst flaw disappears.9m 70 XP
- Linked structuresCircular Linked ListThe tail points back at the head. There is no end — and that's the point.8m 65 XP
Trees
6- TreesBinary Search TreeA tree that keeps one promise — smaller left, bigger right — so it can search fast.12m 95 XP
- TreesTree TraversalsThree ways to visit every node — and why the order matters.10m 80 XP
- TreesHeap & Priority QueueA tree that always keeps the biggest thing on top, ready to grab.11m 90 XP
- TreesAVL TreeA search tree that refuses to become a list — it rotates itself level again.13m 105 XP
- TreesSegment TreeEvery node stores the answer for a whole range — so a range query stops early.13m 110 XP
- TreesTrie (Prefix Tree)Words that start the same share the same path — so autocomplete is free.12m 100 XP
Graphs
7- GraphsBreadth-First SearchExplore a network in rings, nearest first — using a queue.11m 95 XP
- GraphsDepth-First SearchPlunge down one path to the end, then back up and try the next.10m 90 XP
- GraphsTopological SortPut jobs in an order where nothing happens before what it depends on.10m 90 XP
- GraphsDijkstra's Shortest PathThe cheapest route through a weighted map — always finish the nearest place first.14m 110 XP
- GraphsBellman–FordSlower than Dijkstra, and it can do the one thing Dijkstra can't.13m 105 XP
- GraphsA* SearchDijkstra with a sense of direction — it guesses what's left, and aims.13m 110 XP
- GraphsUnion-FindMerge groups and ask 'are these two connected?' — in effectively constant time.12m 100 XP
Core techniques
7- Core techniquesRecursion & the Call StackA function that calls itself — and the pile of calls that piles up.12m 90 XP
- Core techniquesTwo PointersTwo markers moving toward each other turn an O(n²) search into O(n).9m 75 XP
- Core techniquesSliding WindowReuse the last answer instead of recomputing — a window that slides, not restarts.9m 75 XP
- Core techniquesMonotonic StackA stack kept in order — so one new value can answer many old questions at once.11m 95 XP
- Core techniquesGreedy AlgorithmsAlways take the best-looking option right now — and sometimes that's provably optimal.11m 90 XP
- Core techniquesBacktrackingGuess, explore, and when it dead-ends — put it back exactly as it was.13m 105 XP
- Core techniquesDynamic ProgrammingSolve each small problem once, write the answer down, and never solve it again.15m 120 XP