Hi, I'm Gayle Laakmann McDowell, author of Cracking the Coding Interview. Today I'm going to build a comparator that we can use to
sort an array. So a lot of interview questions are almost annoyingly abstract.
This one is actually super applicable. There's a lot of reasons why you might
want to implement your own comparator and one of the most common reasons is that
you're sorting some, an array of some type, and the computer doesn't know how
to sort it unless you tell it. So it doesn't know how to pick which element should
appear first. And that's what this case is. So we have this player class and we want to
sort it such that the higher scoring person appears first and if they don't,
if they have the same score, then fall back on the names. So let's refresh
ourselves on what this return value of compare means. So here's what it means. We
should return a negative value if we want X to appear first, 0 if they can appear in either order, and a positive value if X is considerably
bigger and than Y. So here our logic is, we want to say if they have the same score
then use the names. Otherwise we want to say if a dot score is
bigger than b dot score then we actually want to return negative 1, then a should
appear first. Otherwise, return 1. So we can do this and
this works here but there's actually a simpler or shorter way of doing it
anyway. We can do return b dot score minus a dot score, so note here that, I'm gonna write
this, if x should appear first x should appear a second. So note here that the sign is what
matters, the actual value doesn't matter. So doing this will give a
consistent sign with this one because note that a dot scorer is bigger than b dot
score, this value will in fact be negative. If a dot score is smaller than
b dot score than this value will be positive. So it gives a consistent sign
with this longer bit of code. So that's all we have to do. Now let's talk about
falling back on the names here. Well a really simple way of doing this
is, you know, actually just fall back on the names. So return whatever, return, just use the string comparison. So return string dot compared to, or a dot name dot
compare to b dot name. And that's as simple as it is. So if you look at how different compare operations are, methods are written, you'll see this kind
of logic a lot where we do subtraction. So it's a useful kind of tip to know it
can make your code a little bit shorter and cleaner so this is a really useful
thing to know how to do, if not for your in your interviews then at least for
real life. There's, the syntax will of course vary from language to language,
but most languages should, at least most modern languages should have some sort
of concept like this, where you can give a, give the built-in sorting algorithm
some way of sorting a type that otherwise wouldn't know how to type. So
look this up in whatever language you're going to be using. Super useful for a lot of
different situations. Good luck.
