Programmer's conundrums

[Chuck Guzis]

I recall that one test we'd use on new assembly language programmers on the
CDC 6000 series was a routine to save the contents of all of the registers
without using an exchange jump.  It's much harder than it appears to be at
first.  No register assumptions like B1=1 allowed, either.

Are there any similar tasks on other architectures that try a programmer's
mettle?

Cheers,
Chuck