Dummu - Algorithm in Regex

The brute-force version works fine until the input size stops being small.

Why this matters for Regex

This is a bold claim, an italic aside, and an underlined point, all in one Regex example.

What it touches:

• The Regex runtime or interpreter
• Whatever calls the code around it
• Anyone reading this six months from now

How to apply it:

1. Read the snippet below once, slowly.
2. Try changing one value and predict the output before running it.
3. Compare your prediction against what actually happens.

"Big O is not academic. It is the difference between instant and unusable at scale."

'2026-08-26'.match(/^(\d{4})-(\d{2})-(\d{2})$/);
// ['2026-08-26', '2026', '08', '26']

Reference: Regex documentation

Big O is not academic. It is the difference between instant and unusable at scale.