Question 1

What is a common email validation regex?

Accepted Answer

/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/ — This is the RFC 5322 simplified email pattern.

Question 2

What is catastrophic backtracking?

Accepted Answer

It occurs when a regex with nested quantifiers (like (a+)+ ) causes exponential time complexity on certain input strings. Always test patterns with long inputs. Avoid nested quantifiers on the same characters.

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