Markdown Parser

Level: Advanced 60–90 min

Concepts: AlgorithmsEdge CasesBoundariesRefactoring

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Build a parser that converts a subset of Markdown to HTML, one feature at a time.

Requirements

Implement the following Markdown features in order. Each step builds on the previous — add one feature at a time using TDD.

1. Paragraphs — plain text becomes <p>text</p>
2. Bold — **text** becomes <strong>text</strong>
3. Italic — _text_ becomes <em>text</em>
4. Headers — # text becomes <h1>text</h1>, ## text becomes <h2>text</h2> (support h1-h6)
5. Links — [text](url) becomes <a href="url">text</a>
6. Unordered lists — lines starting with - become <ul><li>text</li></ul>

Test Cases

Input	Output
Hello	<p>Hello</p>
**bold**	<p><strong>bold</strong></p>
_italic_	<p><em>italic</em></p>
**bold** and _italic_	<p><strong>bold</strong> and <em>italic</em></p>
# Heading	<h1>Heading</h1>
## Sub Heading	<h2>Sub Heading</h2>
###### Smallest	<h6>Smallest</h6>
[click](http://example.com)	<p><a href="http://example.com">click</a></p>
**_bold italic_**	<p><strong><em>bold italic</em></strong></p>
“	“ (empty string)
#No space	<p>#No space</p> (not a header — no space after #)

List Example

Input:

- item one
- item two
- item three

Output:

<ul><li>item one</li><li>item two</li><li>item three</li></ul>

Bonus

• Add inline code — `code` becomes <code>code</code>
• Add code blocks — triple backtick blocks become <pre><code>text</code></pre>
• Add blockquotes — > text becomes <blockquote>text</blockquote>
• Handle multiple paragraphs — blank lines separate paragraphs
• Handle escaped characters — \*not bold\* renders as literal asterisks