hedgeye-bnovak

Given the following hash
h = {a: 1, b1: {b2: {b3: nil}, c2: nil}, c1: {c2: {c3: nil}}}

Write a function that prints out all the keys, in order of their keys (not alphabetical order)
i.e. a, b1, b2, b3, c2, c1, c2, c3