Table of Contents

• Background
• Fork & Attribution
• Fundamentals
• Notes
• Question List
• Google Drive Progress Sync
• Solutions
• Contributing
• Suggestions
• Acknowledgements

Background

This repo is intended for any individual wanting to improve their problem solving skills for software engineering interviews.

Problems are grouped under their respective subtopic, in order to focus on repeatedly applying common patterns rather than randomly tackling questions.

All questions are available on leetcode.com with some requiring leetcode premium.

Fork & Attribution

This repository is a fork/adaptation of Sean Prashad's Leetcode Patterns. The original project and question list are credited to Sean Prashad.

This fork is maintained by Justin Mathew at mathewjustin/leetcode-patterns and includes modifications such as a local pattern study UI, debug drills, offline/local-first progress support, and integration with Justin's blog at justinmathew.com/leetcode-patterns.

The original work is licensed under the Creative Commons Attribution-NonCommercial 4.0 International License. This fork preserves that attribution and indicates that changes have been made. This project is intended for non-commercial interview preparation and study use.

Fundamentals

To find the greatest amount of success when practicing, it is highly recommended to know the methods and runtimes of the following data structures and their operations:

• Arrays
• Maps
• Linked Lists
• Queues
• Heaps
• Stacks
• Trees
• Graphs

In addition, you should have a good grasp on common algorithms such as:

• Breadth-first search
• Depth-first search
• Binary search
• Recursion

Notes

This pdf contains information for the main data structures in Java.

Other useful methods to know include substring(), toCharArray(), Math.max(), Math.min(), and Arrays.fill().

Question List

The original question list can be found here: https://seanprashad.com/leetcode-patterns/.

This fork is published here: https://justinmathew.com/leetcode-patterns/.

Google Drive Progress Sync

Study progress is local-first. Completed questions, stars, notes, solved dates, and reminders are stored in localStorage and can optionally sync to a user's Google Drive.

The sync layer uses the Google Drive appDataFolder scope, which creates a hidden JSON file named justin-leetcode-patterns-store.v1.json that only this app can read or write. The document is versioned and organized by namespace:

{
  "version": 1,
  "app": {
    "id": "leetcode-patterns",
    "name": "LeetCode Patterns",
    "updated_at": "2026-06-02T00:00:00.000Z"
  },
  "namespaces": {
    "progress": {
      "version": 1,
      "updated_at": "2026-06-02T00:00:00.000Z",
      "data": {
        "completed": [],
        "starred": [],
        "notes": {},
        "solved_dates": {},
        "reminders": {}
      }
    },
    "personal_tips": {
      "version": 1,
      "updated_at": "2026-06-09T00:00:00.000Z",
      "data": {
        "items": [],
        "updated_at": "2026-06-09T00:00:00.000Z"
      }
    }
  }
}

Built-in programming tips remain part of the app and are read-only. Tips created by the user are stored under personal_tips, where they can sync privately across browsers. New data types should be added as new namespaces, for example debug_drills, interview_sessions, settings, or spaced_repetition, instead of mixing them into the progress payload.

To enable sync, create a Google OAuth web client and set NEXT_PUBLIC_GOOGLE_CLIENT_ID for the deployment. The mounted blog build also needs this value because it rebuilds this app before publishing /leetcode-patterns/.

Solutions

Solutions written in Java can be found in the solutions branch.

Contributing

The app is built with Next.js (App Router), React 19, TypeScript, Tailwind CSS v4, TanStack Table v8, Lucide React for icons, and Google Analytics via @next/third-parties. Tests use Vitest + React Testing Library.

npm install
npm run dev         # app: http://localhost:3000, Excalidraw: http://localhost:8080
npm test            # single run
npm run test:watch  # watch mode

A local Excalidraw container starts automatically with npm run dev. It uses Docker's unless-stopped restart policy, so it also returns when Docker starts after a reboot. Use npm run excalidraw:stop to stop it explicitly and npm run excalidraw:start to start it again.

A Husky pre-push hook runs npm test automatically before every push. This is set up for every clone via the prepare script.

Acknowledgements

Original project: Sean Prashad's Leetcode Patterns.

This list is heavily inspired from Grokking the Coding Interview with additional problems extracted from the Blind 75 list and this hackernoon article on 14 patterns to ace any coding interview question.