CC BY-NC-SA 4.0 License Terms for hello-algo: Usage Rights and Compliance Guide

The hello-algo repository is released under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) license, which permits free study and adaptation of the algorithmic code provided you give proper attribution, avoid commercial use, and share derivatives under identical terms.

The krahets/hello-algo repository provides comprehensive algorithm implementations and educational content for developers worldwide. Understanding the CC BY-NC-SA 4.0 license terms is essential for anyone reusing the code examples or documentation, as this license governs how you can legally share, modify, and distribute the material.

Core CC BY-NC-SA 4.0 License Requirements

The license imposes four fundamental obligations that govern how you can use the code and content from the repository.

Attribution (BY)

You must give appropriate credit to the original author when sharing or adapting the material. According to lines 44-53 of the LICENSE file, this requires retaining:

• Identification of the creator (the repository owner)
• A copyright notice
• A notice referring to the Public License
• A URI or hyperlink to the Licensed Material
• Indication of any changes you made

Failure to provide this attribution constitutes a breach of license terms.

NonCommercial Use (NC)

You may not use the material for commercial advantage or monetary compensation. As stated in lines 60-62 of the LICENSE file, you may reproduce and share the Licensed Material for NonCommercial purposes only. This restriction applies to derivative works, meaning you cannot incorporate hello-algo code into products you sell or services that generate revenue without obtaining separate permission from the author.

ShareAlike (SA)

If you create Adapted Material by modifying code snippets or documentation, you must release your adaptation under the same CC BY-NC-SA 4.0 license. Lines 86-89 of the LICENSE file specify that you must apply a Creative Commons license with the same License Elements (BY-NC-SA). You cannot apply more restrictive terms or proprietary licenses to your derivative works.

No Additional Restrictions

You may not impose extra legal terms or technological measures that restrict others from exercising the rights granted by the license. According to lines 97-99 of the LICENSE file, you cannot offer or impose any additional terms that restrict exercise of the Licensed Rights.

Legal Rights and Protections

The license document outlines specific legal protections and the scope of rights granted to users.

Scope of License Grant

You receive a worldwide, royalty-free, non-sublicensable, non-exclusive, irrevocable license to reproduce, distribute, and adapt the material, as detailed in lines 55-58 of the LICENSE file. These rights apply provided you adhere to the attribution, non-commercial, and share-alike conditions.

Disclaimer and Liability

The material is provided as-is without warranties of any kind. Lines 127-134 of the LICENSE file disclaim all liability for damages arising from use of the Licensed Material. The licensor offers the work without warranty of fitness for a particular purpose or merchantability.

Termination and Reinstatement

If you breach any term of the license, your rights terminate automatically. However, as stated in lines 156-167 of the LICENSE file, your rights can be reinstated if you correct the breach within 30 days of discovering the violation.

Practical Compliance for Code Reuse

When incorporating hello-algo code into your projects, follow these specific practices to maintain compliance.

Attribution Header Template

Add the following header comment to any file containing reused code:

/**
 * © 2024 Krahets – hello-algo
 * Code derived from https://github.com/krahets/hello-algo
 * Licensed under CC BY-NC-SA 4.0 (https://creativecommons.org/licenses/by-nc-sa/4.0/)
 * Modifications: <list changes here>
 */

Commercial Use Restrictions

Do not deploy hello-algo code in products that you sell, subscription services that generate revenue, or internal tools used for commercial profit. Educational projects, personal portfolios, and academic research qualify as permitted non-commercial uses.

Derivative Work Requirements

When modifying code from codes/javascript/modules/Vertex.js or codes/csharp/utils/TreeNode.cs, you must:

• Document all changes in the header comments
• Release your modified version under CC BY-NC-SA 4.0
• Include the same attribution information
• Not apply proprietary licenses or DRM to your adaptations

Implementation Examples for Proper Attribution

These examples demonstrate compliant reuse of hello-algo code in different programming languages.

JavaScript Example (Vertex.js)

When adapting the Vertex class from codes/javascript/modules/Vertex.js, include this attribution header:

/**
 * Vertex class – adapted from hello‑algo
 * Original source: https://github.com/krahets/hello-algo/blob/main/codes/javascript/modules/Vertex.js
 * License: CC BY‑NC‑SA 4.0 (https://creativecommons.org/licenses/by-nc-sa/4.0/)
 *
 * Modifications:
 *   – Added TypeScript type annotations
 *   – Exported as ES6 module
 */

export class Vertex {
  constructor(value) {
    this.value = value;
    this.neighbors = [];
  }

  addNeighbor(vertex) {
    this.neighbors.push(vertex);
  }
}

C# Example (TreeNode.cs)

For the TreeNode class from codes/csharp/utils/TreeNode.cs, use this format:

// TreeNode.cs – adapted from hello‑algo
// Source: https://github.com/krahets/hello-algo/blob/main/codes/csharp/utils/TreeNode.cs
// License: CC BY‑NC‑SA 4.0 (https://creativecommons.org/licenses/by-nc-sa/4.0/)

public class TreeNode<T> {
    public T Value { get; set; }
    public List<TreeNode<T>> Children { get; } = new List<TreeNode<T>>();

    public TreeNode(T value) {
        Value = value;
    }

    public void AddChild(TreeNode<T> child) => Children.Add(child);
}

Both examples credit the original author, link to the exact source file, state the CC BY-NC-SA 4.0 license, and document modifications.

Key Repository Files

Understanding the license requires referencing these specific files in the krahets/hello-algo repository:

• LICENSE — Contains the full legal text of the CC BY-NC-SA 4.0 license applied to the entire repository, including specific clauses regarding attribution (lines 44-53), non-commercial use (lines 60-62), and share-alike requirements (lines 86-89).

• README.md — Provides high-level project description and references the licensing terms.

• codes/javascript/modules/Vertex.js — Representative source file demonstrating how attribution headers should be formatted when reusing JavaScript implementations.

• codes/csharp/utils/TreeNode.cs — C# utility class example showing proper attribution for .NET adaptations.

Summary

The CC BY-NC-SA 4.0 license governing the hello-algo repository establishes these key requirements:

• Attribution is mandatory — You must credit the original author (Krahets), provide a link to the repository, and indicate any changes made.
• Commercial use is prohibited — You cannot use the code in products, services, or applications that generate revenue or provide commercial advantage.
• Derivatives must be shared alike — Any modified versions must be released under the identical CC BY-NC-SA 4.0 license without additional restrictions.
• Compliance is actionable — Include attribution headers in source files, link to the license text, and ensure your use case qualifies as non-commercial.

Frequently Asked Questions

Can I use hello-algo code in my commercial startup or SaaS product?

No. The CC BY-NC-SA 4.0 license explicitly prohibits commercial use. According to lines 60-62 of the LICENSE file, you may only reproduce and share the material for NonCommercial purposes. Using the code in a revenue-generating product, subscription service, or commercial application constitutes a license breach that terminates your rights automatically.

What happens if I modify the code but don't share it under the same license?

If you create derivative works (Adapted Material) and share them without applying the CC BY-NC-SA 4.0 license, you violate the ShareAlike requirement specified in lines 86-89 of the LICENSE file. This breach causes your license rights to terminate immediately. You must either apply the same license to your modifications or cease distribution of the derivative work.

How do I properly attribute the original author when copying a single function?

You must include a header comment that identifies the creator (Krahets), links to the original repository (https://github.com/krahets/hello-algo), references the CC BY-NC-SA 4.0 license, and documents any changes. As demonstrated in the Vertex.js and TreeNode.cs examples, place this attribution at the top of the file containing the reused code to satisfy the requirements in lines 44-53 of the LICENSE file.

Can I restore my license rights after accidentally violating the terms?

Yes, but only if you act within the cure period. According to lines 156-167 of the LICENSE file, if your license terminates due to a breach, your rights can be reinstated automatically if you correct the violation within 30 days of discovering it. If you fail to cure the breach within this window, you must obtain express permission from the licensor to restore your rights.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}