Booking.com Developer interview questions

You have a function f(p) that returns an array of linked pages e.g f(homepage) = {page1, page2, page3}. Or f(page1) = {page4, page5}. If there is no linked pages function will return null. And we say one site is a good site if we can get to any page of that site in a less than 6 clicks. The task was to write a function that will check is it a good site or not using f(p).