▶ Open the course — runs in your browser, nothing to install.
An interactive algorithms course for people starting from zero. Decision trees, DP tables and shrinking intervals are replayed frame by frame, so you watch the state change instead of trying to hold it in your head.
Sister site: DataData (data structures). The split is deliberate — techniques that hang off a specific structure (two pointers, sliding window, BFS/DFS, monotonic stacks) live there; the general problem-solving strategies live here.
The course home — 13 chapters from sorting to string matching
Sorting, replayed frame by frame
| # | Chapter | What it covers |
|---|---|---|
| 00 | Prologue | Correct first, then fast · recursion as the foundation · complexity tiers |
| 01 | Sorting | The three simple sorts, merge, quicksort, the comparison lower bound, what your language actually uses |
| 02 | Divide and conquer | The master theorem, LC 50 / 23 / 53 |
| 03 | Binary search | Interval conventions, boundary templates, searching the answer space |
| 04 | Bit manipulation | Masks, subsets, XOR tricks, cross-language pitfalls |
| 05 | Backtracking | One decision tree behind subsets, combinations and permutations; pruning and dedup |
| 06 | Greedy | When greed is provable — the exchange argument, and when it fails |
| 07 | Dynamic programming | State, transition, initialization, order — the four questions |
| 08 | Knapsack | 0/1, unbounded, bounded; the rolling array and why the direction matters |
| 09 | Sequence DP | LCS, edit distance, LIS with binary search |
| 10 | Advanced DP | State machines, interval DP, bitmask DP |
| 11 | Math | Modular arithmetic, GCD, sieves, fast power, game theory |
| 12 | Strings | KMP, the next array, Rabin-Karp, Manacher |
| ✦ | Atlas | A decision map across both sites: signal → technique |
Each chapter follows the same rhythm: an intuition first, then a frame-by-frame visualization, then code in Java / Python / JavaScript, then the interview follow-ups, then a quiz. Progress is stored locally in the browser.
Requires Node 22 (an .nvmrc is included):
nvm use
npm install
npm run dev # http://localhost:3000Build with type checking: npm run build.
Next.js 15 (App Router) + TypeScript + React 19, plain CSS. No API routes, so everything prerenders to static pages.
Each chapter is one folder under app/ holding its page, its visualizations (viz.tsx) and
its own stylesheet, paired with a data file under lib/ for the problem sets. Frames are
precomputed at module load — buildXxx(): Frame[] — and the component only renders frame i.
Shared pieces: the stepper in lib/stepper.tsx, the graph renderer, the quiz component,
progress tracking in lib/progress.tsx, and the chapter registry in lib/curriculum.ts
(the sidebar, command palette, prev/next links and progress all derive from it).
© 2026 Weiren Feng. All rights reserved. Published for reading and portfolio purposes; not licensed for reuse, modification, or redistribution.