Practice problems

Two formats: structured problems run in an in-browser sandbox with a built-in AI assistant; open-ended problems you build in your own editor with your own AI tools.

Structured · in-browser sandbox

Battleship

easy

Track ship placement and attack resolution on a board, data structure design with a bug → feature → scale arc.

Data Structures

45 min

Inventory Packer

easy

Pack items with weights into bins with capacities, greedy bin packing with a bug → feature → scale arc.

Greedy / Packing

45 min

Spell Checker

easy

Suggest corrections ranked by edit distance, string matching with a bug → feature → scale arc.

String / ParsingDynamic Programming

45 min

Card Game

medium

Manage a deck and simulate a trick-taking hand, data structure design and simulation with a bug → feature → scale arc.

Data Structures

50 min

Friend Recommender

medium

Recommend people by shared connections, graph search with a bug → feature → scale arc.

Graph Search

50 min

Maze Solver

medium

Find the shortest path through a grid with obstacles, graph search with a bug → feature → scale arc.

Graph Search

50 min

Release Radar

medium

A follow-and-notify service where the notifications never arrive and the unread badge lies — an API-contract debugging arc.

API Contracts

50 min

Route Planner

medium

Weighted routing across a transport network with transfers, graph search with a bug → feature → scale arc.

Graph Search

55 min

Task Scheduler

medium

Run dependent tasks in order and fail on cycles, topological sort with a bug → feature → scale arc.

Topo Sort

55 min

Word Container

medium

Store words and search them by prefix and in a grid, data structure design and string matching with a bug → feature → scale arc.

Data StructuresString / Parsing

55 min

Connect Four

hard

Win detection, move validation, and a depth-limited AI opponent, backtracking and game-state design with a bug → feature → scale arc.

BacktrackingData Structures

60 min

Kitchen Orders

hard

Assign orders to stations under priority and timing constraints, greedy scheduling and priority queues with a bug → feature → scale arc.

Greedy / PackingTopo Sort

60 min

Maximize Unique Characters

hard

Maximize the number of distinct characters by choosing and swapping, greedy plus backtracking with a bug → feature → scale arc.

Greedy / PackingBacktracking

60 min

Nonogram Solver

hard

Solve a nonogram by constraint satisfaction over row clues, backtracking with propagation, with a bug → feature → scale arc.

Backtracking

60 min

Open-ended · your editor

Fileshare

medium

A tiny REST file-sharing service, upload, list, download, expiring links. Low-level design with AI as your accelerator.

Data Structures

60 min

Gridbot

medium

A command language moves a bot around an obstacle grid, with pathfinding to a target, parsing plus graph search, built from scratch.

String / ParsingGraph Search

45 min

LinkLock

medium

A URL shortener with custom slugs, expiry, and click analytics, data structure design under constraints.

Data StructuresString / Parsing

60 min

LRU Cache

medium

Build an LRU cache with get/put in O(1), hash map plus doubly linked list, tested against a starter harness.

Data Structures

30 min

Transcribe

medium

A job pipeline that processes text-transformation jobs with retries and concurrency, queues and failure handling from scratch.

Dynamic ProgrammingGreedy / Packing

60 min

Collaborative Editor

hard

Concurrent text edits merged without corruption, last-write-wins and OT-lite conflict resolution from scratch.

Data Structures

60 min

Schedulr

hard

A meeting and task scheduler that honors dependencies and availability, topological ordering plus interval scheduling.

Topo SortGreedy / Packing

60 min