How do I select an element that only has the one specified class? [duplicate]

If I have two elements like this

<div class="one two three"></div> <div class="one"></div>

And I want to grab the div that has only the "one" classname.

I know I can do this like this:

div[class="one"]

because if I do div.one it applies to both,

is there any other way to get the element with just the specified classname?

edit - the goal being to shorten the selector character count