The Scenario

You are building a data validation pipeline that processes user-submitted strings before parsing them. To prevent malicious input, you run a local Python validator to check patterns before further processing.

The Incident

A user pasted a malformed pattern string into your API. Suddenly, your backend froze. No errors, no crash logs—just 100% CPU usage. Your downstream services are sitting idle, but your validation container is completely unresponsive.

The Stakes

• The Victim: Your validation service.
• The Culprit: A regex validator intended to check for repeating character patterns.
• The Result: A "ReDoS" (Regular Expression Denial of Service) that forces your CPU to check millions of paths for a single string.

The Goal

Patch the validate_pattern function.

• The current logic uses ^((A+)+)+$ which has O(2^n) complexity.
• Your Task: Rewrite the regex to accept valid patterns instantly (under 10ms) without hanging on malformed inputs.