Interview Notes Code Repository

A curated collection of Java coding solutions, algorithms, and reference implementations created from real interview practice. This repository is structured as a Maven project with Spring Boot support, and contains categorized solutions by year/month/assessment as well as domain-focused examples (e.g., Amazon-style problems, data structures, concurrency, web, etc.).

Table of Contents

• Overview and Goals
• Tech Stack
• Project Layout
• Quick Start
• Build and Run
• Testing
• Coding Guidelines and Conventions
• Notable Modules and Examples
• Troubleshooting
• How to Contribute
• FAQ
• License

Overview and Goals

This project serves as a living knowledge base of interview-oriented code:

• Ready-to-run Java programs for algorithmic problems and assessments.
• Clean, well-documented approaches that highlight edge cases, correctness, and performance.
• Reusable utilities for HTTP, parsing, collections, and testing.
• Spring Boot app scaffolding for web APIs and experimentation.

Tech Stack

• Java 17
• Maven + Spring Boot (2.x line)
• JUnit 4 and Spring Boot Test
• Popular libraries used where relevant (Gson, Apache Commons, Kafka clients, Redis Jedis, WebFlux)

Key dependencies are defined in pom.xml.

Quick Start

1. Clone and enter the project directory: git clone cd interview-notes-code
2. Ensure prerequisites:
   • Java 17 (java -version)
   • Maven 3.8+ (mvn -version)
3. Build and run tests: mvn clean install
4. Run a sample class (e.g., Solution.java): mvn -Dexec.mainClass=com.interview.notes.code.year.y2025.september.assesment.test6.Solution
   -Dexec.classpathScope=runtime
   org.codehaus.mojo:exec-maven-plugin:3.1.0:java

Tip: You can also run any class with a main method directly from your IDE.

Project Layout

Root-level key files/directories:

• pom.xml: Maven configuration
• src/main/java: Source code
• src/test/java: Unit and integration tests
• src/main/resources: App resources (static, templates)
• README.md: This document
• HELP.md: Maven/Spring getting started references

Within src/main/java the code is organized by packages indicating year/month/assessment and topic areas. Examples:

• com.interview.notes.code.year.y2025.september.assesment.test6
  • Solution.java: An end-to-end solution fetching and processing paginated API data, including robust filtering and tie-breaking rules, with a main method for quick manual tests.
  • BooleanCheck.java, ConsoleOutputCheck.java: Utility checks used in assessments.
• com.interview.notes.code.amazon
  • NumberofAirplanesSkyTest.java, Interval.java, CustomQueue.java: Practice problems inspired by Amazon interview patterns.

This convention keeps historical problems and company-specific practice exercises separated while allowing reuse of shared utilities.

Build and Run

Prerequisites:

• Java 17 installed and available on PATH
• Maven 3.8+ installed

Common commands (run from repository root):

• Build (compile + test): mvn clean install
• Run Spring Boot app (if needed): mvn spring-boot:run
• Execute a specific main class directly (example): mvn -Dexec.mainClass=com.interview.notes.code.year.y2025.september.assesment.test6.Solution
  -Dexec.classpathScope=runtime
  org.codehaus.mojo:exec-maven-plugin:3.1.0:java

Alternatively, many solutions include a public static void main(String[] args) entry point and can be executed from your IDE.

Testing

• To run all tests: mvn test
• Surefire reports will be available in target/surefire-reports.
• For individual tests, use your IDE’s test runner or mvn -Dtest=FullyQualifiedTestName test.

Code Formatting

• This project uses Google Java Format via the fmt-maven-plugin to keep Java code consistent.
• To format the code automatically:
  • Using Maven directly: mvn com.coveo:fmt-maven-plugin:format
  • Or using the helper script: ./scripts/format.sh
• To fail the build if formatting is needed: mvn com.coveo:fmt-maven-plugin:check

Git: Commit and Push

You can commit and push your changes with the following commands. Make sure you have a GitHub repository created and that your local repo has a remote set.

1. Configure Git (once per machine): git config --global user.name "Your Name" git config --global user.email "[email protected]"

2. Initialize repo (if not already): git init

3. Add a remote (replace with your repository URL): git remote add origin https://github.com//.git

   or use SSH

   git remote add origin [email protected]:/.git

4. Stage, commit, and push: git add -A git commit -m "chore: format code and update README" git push -u origin main

   If your default branch is master, use master instead of main.

Notes:

• Pushing to GitHub requires that you have permission and are authenticated. For HTTPS, use a Personal Access Token ( PAT) as your password if prompted. For SSH, ensure your SSH key is added to your GitHub account.
• From this automated environment, we cannot directly push to your GitHub without your credentials. Run the above commands locally to push.

Coding Guidelines and Conventions

• Prefer clear, readable solutions with comments explaining business rules and edge cases.
• Use immutable data where possible and avoid side effects.
• Handle nulls defensively; fail closed, not open.
• Include tie-breaker rules and deterministic ordering if required by problem statements.
• Add simple smoke tests or a lightweight test harness in classes that interact with external services.
• Keep methods small and single-purpose; favor pure functions for algorithmic problems.

Notable Modules and Examples (Deep Dive)

1. API Pagination + Filtering Example: Solution.java

• Location: com.interview.notes.code.year.y2025.september.assesment.test6.Solution
• Problem: Find the longest-duration event organized by a given organizer that matches a specific genre.
• Highlights:
  • Uses Java HttpClient and Gson to fetch and parse paginated JSON from https://jsonmock.hackerrank.com/api/events.
  • Case-insensitive matching of organizer and genre.
  • Robust comparator: duration (null treated as 0) descending, tie-break by id ascending.
  • Returns "-1" on missing matches or any network/parse errors.
  • Includes a test() method for quick checks and a main() entry point for manual runs.
• Example run (console): mvn -Dexec.mainClass=com.interview.notes.code.year.y2025.september.assesment.test6.Solution
  -Dexec.classpathScope=runtime
  org.codehaus.mojo:exec-maven-plugin:3.1.0:java

2. Amazon-style Problems:

• NumberofAirplanesSkyTest.java and Interval.java demonstrate interval merging/scanline ideas.
• CustomQueue.java shows building a queue with custom constraints helpful in DS interviews.

Run Individual Examples (Common)

You can run any class with a public static void main(String[] args) using the Exec Maven Plugin. Below are some handy examples from recent additions:

• Payment processing demo (common/test4/Main): mvn -Dexec.mainClass=com.interview.notes.code.year.y2025.september.common.test4.Main
  -Dexec.classpathScope=runtime
  org.codehaus.mojo:exec-maven-plugin:3.1.0:java

• Third highest number finder (common/test4/ThirdHighestNumberFinder): mvn -Dexec.mainClass=com.interview.notes.code.year.y2025.september.common.test4.ThirdHighestNumberFinder
  -Dexec.classpathScope=runtime
  org.codehaus.mojo:exec-maven-plugin:3.1.0:java

• Longest unique substring tester (common/test6/LongestUniqueSubstringTester): mvn -Dexec.mainClass=com.interview.notes.code.year.y2025.september.common.test6.LongestUniqueSubstringTester
  -Dexec.classpathScope=runtime
  org.codehaus.mojo:exec-maven-plugin:3.1.0:java

Tip: If the package path changes over time (e.g., new month/year folders), adjust the -Dexec.mainClass accordingly, or run directly from your IDE.

Push to GitHub

Follow these steps to push this project to your GitHub repository.

1. Initialize Git (if not already a repo): git init

2. Create a new empty repository on GitHub (do not add README/License). Copy its URL, e.g.: https://github.com//.git

3. Add remote and set the default branch name (main): git remote add origin https://github.com//.git git branch -M main

4. Commit and push your changes: git add -A git commit -m "Initial commit" git push -u origin main

Alternatively, use the helper script included in this repo:

• First time (sets origin and pushes to main): scripts/push.sh "Initial commit" https://github.com//.git main

• Subsequent pushes (origin already set): scripts/push.sh "Update: "

Notes:

• Make sure you are authenticated with GitHub (HTTPS with Personal Access Token or SSH).
• The .gitignore in this repo excludes build artifacts (target/), IDE files, OS files, and other non-source items.

How to Contribute

• Fork the repository and create a feature branch.
• Follow the coding guidelines above.
• Include comments and small test cases to explain tricky parts.
• Open a pull request with a clear description of changes and rationale.

Troubleshooting

• Maven cannot find Java 17:
  • Ensure JAVA_HOME points to JDK 17 and your PATH uses that JDK (java -version should show 17).
• Tests fail due to ports in use (for any web tests):
  • Stop other local servers or set a different server.port in application.properties.
• SSL/network errors when running API-based examples:
  • These examples depend on public endpoints; retry later or ensure your network allows outbound HTTPS.
• Exec plugin error when running a main class:
  • Ensure the exec-maven-plugin goal specified in the command matches the version declared in the README (3.1.0 in examples).

FAQ

• Q: Can I run a single solution without the Spring Boot app? A: Yes. Many classes contain a main method. Use the Exec Maven Plugin example above or run via IDE.
• Q: Do I need internet access for some solutions? A: Only for problems that intentionally call public APIs (e.g., Solution.java). Others are self-contained.

License

If a LICENSE file exists at the repository root, the project is distributed under that license. If not, treat the code as All Rights Reserved by the repository owner unless otherwise specified.

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Last updated: 2025-09-18