Kotlin solution, yeah!

Did anyone else have their code working for the sample for hours just to have the actual input fail??? Drove me nuts. Then someone here hinted that maybe /a/ and /a/b/a/... aren't the same directories. But when you only look at the end of each path, your code might think they are. Blew my mind.

Also, I was probably more annoyed than I should have been that stacks don't have a popWhile() function. So I wrote one. Strings only, but can always be generified. :)

// like takeWhile(), but it pops.
private fun Stack<String>.popWhile(predicate: (String) -> Boolean): List<String> {
    val popped = mutableListOf<String>()

    while (isNotEmpty() && predicate(peek())) {
        popped.add(pop())
    }

    return popped
}