Interview Prep

Algorithm practice + theory study notes for backend and fullstack interviews.

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Algorithm Practice

28 TypeScript problems ranked by likelihood, with full test suites and reference solutions.

Quick Start

npm install
npm run ranking        # see all 28 questions ranked by priority
npm run q1             # attempt a question (tests fail until you solve it)
npm run sol:q1         # reveal and run the reference solution

How to Practice

1. Run npm run ranking to see the priority order
2. Open algo/questions/q<N>-*.ts and implement the function
3. Run npm run q<N> to see which tests pass
4. When stuck, run npm run sol:q<N> to see the worked solution

All 28 Questions

Tier 1 — Critical (do these first, ~3h)

#	Title	Pattern	Time
q1	Group Lab Results by Status	Hash Map / Array	20m
q2	Two Sum on Sorted Array	Two Pointers	15m
q3	Longest Unique Substring	Variable Sliding Window	20m
q4	Longest Safe Window (avg ≤ threshold)	Variable Sliding Window	25m
q5	Max K-Window Average	Fixed Sliding Window	20m
q6	Valid Brackets	Stack	15m
q7	Deep Sum of Nested Object	Recursion / DFS	20m
q8	Sort Patients by Multiple Fields	Sorting / Comparators	15m
q9	Binary Search in Sorted Array	Binary Search	15m
q10	Most Common Biomarker Flag	Frequency Map	15m

Tier 2 — Must Solve (~3h, before interview day)

#	Title	Pattern	Time
q11	Longest Abnormal Streak	Sliding Window (streaks)	20m
q12	Patient Queue (FIFO)	Queue / OOP	25m
q13	Flatten Category Tree (BFS)	BFS / Trees	20m
q14	Debug Async Patient Fetcher	Debugging / Async	20m
q15	Parse Health Summary String	String Manipulation	20m
q16	Flatten Nested Record to Dot-Path	Recursion / DFS	25m
q17	Next Greater Reading	Monotonic Stack	25m
q18	Merge Sorted Appointment Schedules	Two Pointers (merge)	30m

Tier 3 — Should Solve

#	Title	Pattern	Time
q19	Anagram Check & Group Anagrams	String / Hash Map	20m
q20	Find First & Last Occurrence	Binary Search (variant)	25m
q21	Memoize + Climb Stairs	DP / Memoization	25m
q22	Three Sum (All Triplets)	Sort + Two Pointers	30m
q23	Reverse Linked List & Detect Cycle	Linked List / Floyd's	20m

Tier 4 — Hard (Staff/Principal level)

#	Title	Pattern	Time
q24	Decode Compressed String	Stack (nested parsing)	30m
q25	LRU Cache	Hash Map + DLL	35m
q26	Minimum Cost Path (Grid DP)	2D Dynamic Programming	35m
q27	Shortest Referral Path (Graph BFS)	Graph / BFS	30m
q28	Minimum Tests (Coin Change DP)	Bottom-up DP	35m

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Theory Study Notes

Tiered Q&A for Java, Spring Boot, React, and Node.js. Ranked by frequency and recency.

File	Topics
notes/java.md	Core Java, concurrency, JVM, Java 21+ features
notes/spring.md	Spring Boot 3, DI, Security, AOT, native image
notes/react.md	React 19, hooks, Server Components, state management
notes/nodejs.md	Event loop, ESM, built-in fetch, performance

Each file has three tiers: Must Know / Good to Know / Nice to Have, with full answers and code examples.

Custom questions live in notes/custom/<tech>.md — they are prepended to the matching tier when notes are regenerated and are never overwritten.

Regenerate Notes

Run the /interview-study skill in Claude Code to scrape fresh content and regenerate all four files:

/interview-study
# optionally: /interview-study focus on java concurrency and react hooks

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Quick-Reference Cheatsheets

short-notes/ contains HTML cheatsheets for fast visual review — open short-notes/index.html in a browser.

Section	Sheets
Database & JPA	ACID, Locking, Indexing, Normalization, N+1, JPA Ecosystem, Views, SQL vs NoSQL
REST API Design	Fundamentals, Patterns, Security & Rate Limiting, Async APIs, Spring Boot example
System Design	Rate Limiter, Consistent Hashing, KV Store, URL Shortener, Chat, News Feed, YouTube, and more
Spring Framework	Dependency Injection, Transactions
Data Structures	Collections & Maps, DS Internals
Frontend & React	React Hooks, useEffect & useCallback

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Tech Stack

• Node.js 22 / ESM modules — TypeScript 5.7 strict mode — tsx runner (no build step)
• Custom test runner — no Jest dependency, mimics TestGorilla output format