Solving a puzzle is a good way of getting attention for your resume. It allows engineers to evaluate your coding skills much better than they would in a phone i

Solving a puzzle is a good way of getting attention for your resume. It allows engineers to evaluate your coding skills much better than they would in a phone interview, it demonstrates interest and ability and geek cred. You can definitely apply without a puzzle, but there's obviously a large number of applicants that do so (and a corresponding signal-to-noise problem).