Assume we are given the problem of say finding all squares modulo $3^4$. Is there any efficient way to compute this without having to check a ton of cases? For just a prime we can use quadratic reciprocity, but that doesn't do any good here.
A problem like this was asked on an oral exam in my program (the number was $4000$, so one had to apply the Chinese remainder theorem first and then solve two questions like this), so I guess the professor thought that this is something that one should be able to work out on the black board pretty quickly.
The only approach I know is to first find all squares modulo say $9$, which would give $0,1,4,7$, then look at the numbers:
and figure out which of these liftings are squares mod $27$. This quickly gets extremely annoying. Especially when having to lift these squares to $3^4$.