In American English, "do" is often left implied. "The same pants as you do" is certainty correct, but "the same pants as you" is much more common.
This also applies to "be", and even native speakers get tripped up on pronouns because of it. You can't see that with the example sentence as given (because "you" is the same form for subject and onject) so let's change it:
She wears the same pants as I (do). She's just as tall as I (am).
Incorrect, but common: She wears the same pants as me. She's just as tall as me.
You wouldn't ever use "me do" or "me am", but with the verb only implied "as" gets misread as a preposition instead of a conjunction.