Airbnb

Build a Todo List

Frontend · List state done right: keys, controlled input, and deletes.

StoreData with Change Listeners

Frontend · A Backbone.Model-style store: two Maps, one event-key normalizer, listeners that can't break each other.

Implement a Promise

Frontend · A one-way state machine, a handler queue, and every callback in a microtask.

Debounce with Cancel and Flush

Frontend · A trailing-edge debounce whose wrapper can also drop the pending call or run it now.

Input Validation

Frontend · Declarative rule factories and one message per field — the first failing rule's.

In-Memory File System

Algorithms & Data Structures · A tree of nodes keyed by path segment — the OOD-style prompt where the implementation is the test.

Pour Water I

Algorithms & Data Structures · Simulate one unit at a time — left, then right, else stay — and land only on strictly lower ground.

Tabs: initTabs(node)

Frontend · A tab UI packaged as an initializer — two independent instances from one function.

Star Rating in a Form

Frontend · Real radio inputs behind the stars: the form submits itself, the keyboard works, N instances are N names.

Shuffle and Deal Five Cards

Frontend · Fisher–Yates, a splice, and fresh nodes per deal — the reveal animation comes free.

Typeahead with Keyboard Navigation

Frontend · Debounce the query, abort the stale request, cache by query, wrap the arrow keys, wire the combobox.

Carousel with a Per-Slide Countdown

Frontend · One interval per slide, one batched update per advance — and the double-advance trap.

Connect Four

Frontend · Immutable board updates, gravity in dropPiece, and a win check that only looks through the last move.

Boxed Sentences I

Algorithms & Data Structures · Greedy word wrap inside ASCII borders — never split a word, never start a line with punctuation.

URL Query-String Parser

Algorithms & Data Structures · Split first, decode second — the ordering that makes the encoded-ampersand case work.

Review Token Tagging

Algorithms & Data Structures · Case-insensitive, longest match wins, original text preserved — a trie walk from every offset.

Retry Wrapper

Algorithms & Data Structures · Pluggable backoff, a retryable filter, hooks, and an abort signal around one loop.

FIFO Order Allocator

Algorithms & Data Structures · Consume the oldest stock first and say which lots an order drew from — an implementation prompt with tie-break rules.

Transfer List

Frontend · Two arrays and one Set of checked ids — get a working version fast, then polish.

Pour Water II

Algorithms & Data Structures · Levels from the top down, one character per column — ground, water, or air.

Abortable Promise

Frontend · Promises can't be cancelled, so cancel the work — and reject once, with an AbortError, only while pending.

Implement Throttle

Frontend · A leading call, then at most one call per window — with a trailing call that carries the latest arguments.

Boxed Sentences II

Algorithms & Data Structures · Each sentence wraps at its own width; one box pads every line to the widest.

Classify a Poker Hand

Algorithms & Data Structures · A rank histogram and two booleans name every category — the ace is the only edge case.