📖 How to Add Problems & Solutions#

This guide covers the complete workflow for adding new problems, marking them solved, and attaching approaches, PDFs, code files, and external solution links.

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How the System Works#

All problems live in one file: _data/problems.yml. Every change you make there automatically propagates to:

• /problems/ — the interactive Problems Hub (searchable, filterable table)
• /learning/dsa/<topic>/<topic>-problems/ — every topic page whose slug matches an entry in the problem’s topics array

You never need to edit topic pages manually to add or update problems.

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Quick Checklist — Adding a New Problem#

1. Open _data/problems.yml
2. Add a new entry block (see schema below)
3. Set topics: to the correct slug(s)
4. Save — it auto-appears everywhere
5. (Optional) Attach a solution/approach link

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problems.yml Schema#

Each entry in _data/problems.yml looks like this:

- id: '1'                          # LeetCode number, or a custom slug like 'gfg-two-sum'
  title: Two Sum                   # Exact problem title
  platform: leetcode               # leetcode | gfg | interviewbit | codeforces
  difficulty: easy                 # easy | medium | hard  (all lowercase)
  topics:                          # list of topic slugs — drives which pages show this problem
    - arrays
    - searching-sorting
  solved: false                    # true once you've solved it
  problem_url: https://leetcode.com/problems/two-sum/
  approach_url: ''                 # written notes, PDF, or external link — see below
  solution_url: ''                 # code file or external solution link — see below

Field reference#

Field	Required	Notes
id	Yes	LeetCode number as string ('1') or custom ('gfg-two-sum')
title	Yes	Displayed as the problem name everywhere
platform	Yes	Source platform
difficulty	Yes	Exactly easy, medium, or hard
topics	Yes	One or more slugs from the recognised list below
solved	Yes	true or false — drives the ✓ Solved badge
problem_url	Recommended	Direct link to the problem statement
approach_url	Optional	Written notes, PDF, or external editorial link
solution_url	Optional	Raw code file or external solution link

Recognised topic slugs#

Slug	Dedicated topic page
arrays	/learning/dsa/arrays/arrays-problems/
strings	/learning/dsa/strings/strings-problems/
linked-list	/learning/dsa/linked-list/linked-list-problems/
tree	/learning/dsa/tree/tree-problems/
stacks	/learning/dsa/stacks/stacks-problems/
searching-sorting	/learning/dsa/searching-sorting/searching-sorting-problems/
sliding-window	No page — filters the hub table only
two-pointers	No page — filters the hub table only

A problem can have multiple topics. It will appear on every matching topic page.

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Attaching Solutions & Approaches#

The Problems Hub generates buttons automatically based on what you put in approach_url and solution_url. The button label and colour are detected from the link type.

Option 1 — Written Editorial (Markdown)#

Best for: written explanations, complexity analysis, diagrams, embedded code.

Step 1. Create a file in the corresponding topic subdirectory inside _editorials/ (e.g., arrays, linked-list):

_editorials/arrays/two-sum-approach.md

Step 2. Add front matter. Crucial: You must include a permalink formatted as /editorials/<slug>/ so the URL remains stable regardless of the subdirectory structure:

---
permalink: /editorials/two-sum-approach/
layout: editorial
title: "Two Sum — Approach"
problem_id: "1"
date: 2025-02-28T12:00:00.000Z
---

Step 3. Write your explanation in Markdown below the front matter.

Step 4. In _data/problems.yml, set:

approach_url: '/editorials/two-sum-approach/'

The hub renders a 📖 Editorial button.

---

Option 2 — Handwritten PDF Notes#

Best for: scanned notebook pages, visual diagrams, hand-drawn trees/graphs.

Step 1. Place the PDF in the relevant topic directory:

_learning/dsa/Arrays/two-sum-notes.pdf

Step 2. In _data/problems.yml, set (path is case-sensitive):

approach_url: '/learning/dsa/Arrays/two-sum-notes.pdf'

The hub renders a 📝 PDF Notes button.

Note: GitHub Pages paths are case-sensitive. /Arrays/ and /arrays/ are different URLs.

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Option 3 — Raw Code File (.cpp, .py, .java, etc.)#

Best for: saving your solution code alongside the problem notes.

Step 1. Save your code file in the topic directory:

_learning/dsa/Arrays/solution-two-sum.cpp

Step 2. In _data/problems.yml, set:

solution_url: '/learning/dsa/Arrays/solution-two-sum.cpp'

The hub renders a 💻 Raw Code button.

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Option 4 — External LeetCode Solution Link#

Best for: linking to a well-upvoted community solution or your own published solution.

Copy the full URL of the solution post and set it in problems.yml:

solution_url: 'https://leetcode.com/problems/two-sum/solutions/123456/my-solution/'

The hub detects the leetcode.com domain and renders a 🔗 Solution button.

Use approach_url for editorial/theory links, solution_url for code-focused links.

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Option 5 — Decap CMS (Netlify Admin UI)#

If you prefer a GUI instead of editing YAML directly:

1. Go to ajdevhub.netlify.app/admin and log in.
2. Click DSA Editorials → New DSA Editorial, write your Markdown, and publish. (Note: Decap CMS may save new editorials to the root of _editorials/. You can move them into topic subdirectories later; just ensure the permalink frontmatter is set).
3. Go to Data Files → DSA Problems Database, find the problem, and paste the slug into approach_url.

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Rules for approach_url vs solution_url#

Scenario	Use
One link covering both explanation and code	approach_url only — leave solution_url empty
Separate editorial + separate code	Both fields
Only raw code, no explanation	solution_url only
Only a LeetCode solution post	Heavy theory → approach_url, mostly code → solution_url

Never point to GitHub blob URLs. Use Jekyll-relative paths (/editorials/..., /learning/...) for internal files.

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Marking a Problem as Solved#

Simply change solved: false to solved: true in _data/problems.yml:

solved: true

The ✓ Solved badge updates on both the Problems Hub and the topic page automatically.

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Complete Example#

A fully-filled entry with a PDF note:

- id: '875'
  title: Koko Eating Bananas
  platform: leetcode
  difficulty: medium
  topics:
    - searching-sorting
    - arrays
  solved: true
  problem_url: https://leetcode.com/problems/koko-eating-bananas/
  approach_url: '/learning/dsa/Searching-Sorting/koko-banana.pdf'
  solution_url: ''

---

Adding a New Topic Page#

If you want a dedicated problems page for a new topic (e.g., graphs):

Step 1. Create _learning/dsa/graphs/graphs-problems.md using this template:

---
layout: default
title: Graphs - Practice Problems
permalink: /learning/dsa/graphs/graphs-problems/
---

{% raw %}{% assign topic_slug = "graphs" %}
{% assign topic_back_url = "/learning/dsa/graphs/" %}
{% assign topic_all    = site.data.problems.problems | where_exp: "p", "p.topics contains topic_slug" %}
{% assign topic_solved = topic_all | where: "solved", true %}
{% assign topic_easy   = topic_all | where: "difficulty", "easy" %}
{% assign topic_medium = topic_all | where: "difficulty", "medium" %}
{% assign topic_hard   = topic_all | where: "difficulty", "hard" %}{% endraw %}

Copy the full structure from any existing topic page such as _learning/dsa/Strings/strings-problems.md and update only the three topic_slug, topic_back_url, and heading values.

Step 2. Register the page in assets/js/problems.js inside topicPages:

const topicPages = {
    // existing entries...
    'graphs': '/learning/dsa/graphs/graphs-problems/',
};

Step 3. Add a chip in problems.md inside the topic-chips div:

<a href="{{ '/learning/dsa/graphs/graphs-problems/' | relative_url }}" class="topic-chip">🕸️ Graphs</a>

Step 4. Add problems with topics: [graphs] in _data/problems.yml and they appear instantly.

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Troubleshooting#

Problem	Cause	Fix
Problem not on topic page	Wrong slug in topics:	Slug must exactly match — linked-list not linked_list
Problem not in hub	YAML syntax error	Check 2-space indentation, no tabs
PDF/code link 404	Path case mismatch	/Arrays/ ≠ /arrays/ — match exactly
Two identical buttons	Same URL in both fields	Put it in one field only
Topic page shows 0 problems	topic_slug mismatch	Ensure the slug in the page matches the slug used in problems.yml
Stale page after changes	_site cache	Run rm -rf _site .jekyll-cache && bundle exec jekyll serve --livereload