Check that HTML tags are balanced — interview question

Given one line of simplified HTML, print YES if every element is closed in the correct (nested) order, otherwise NO.

Rules:

A tag is everything from < to the next >. Text between tags never contains < or >, and neither do attribute values.
<name ...> opens an element and </name> closes it. Tag names are made of letters and digits and are case-insensitive.
Tags starting with <! (comments, doctype) are ignored.
A tag whose content ends with / (like <br/> or <x-icon/>) closes itself.
Void elements never need closing: area base br col embed hr img input link meta source track wbr. A closing tag for a void element (such as </br>) makes the document invalid.

Constraints

The line is at most 20000 characters.

Input and output

Input: One line of HTML.
Output: `YES` or `NO`

Examples

Input 1

<div class="card"><p>Fees<br>₹5,000</p><img src="c.png" alt="campus"></div>

Output

YES

br and img are void elements and need no closing tag.

Input 2

<ul><li>One</ul></li>

Output

NO

The tags close in the wrong order.

Show hints

This is the balanced-brackets problem with tag names as the brackets.
Decide what to do with void, self-closing and comment tags before touching the stack.

Show the explanation

Extract tags with a regex such as /<([^>]*)>/g, and classify each one:

Content starting with ! → ignore.
Starting with / → a closing tag. If its name is void, answer NO. Otherwise the top of the stack must be the same name (compare in lower case); pop it, or answer NO if the stack is empty or holds a different name.
Ending with /, or a void name → nothing to do.
Otherwise → push the lower-cased name.

At the end the stack must be empty (no unclosed elements).

Real browsers are far more forgiving: their parser auto-closes many elements (an unclosed <p> or <li>), which is why validators, linters and JSX compilers are stricter than the browser.

Original UniCircle question. Last reviewed 22 Oct 2026.