So I am watching Potter here. The movie, at least up until where I am, is reasonable true to the book, so consider this a discussion that applies to both the book and the film series.
What I am watching now: The Sorting Hat scene
What is interesting about it: The Sorting Hat toys with putting Harry into Slytherin, either because Harry belongs there, the scar confuses the hat, or the hat is teasing Harry, who is then whispering "not Slytherin" repeatedly. As we know, the hat places Potter in Gryffindor, with his new friends Ron and Hermione.
My question is what would have happened if Harry never ran into Ron and Hermione at the train station, and did not learn the basics of the four houses during his encounters with them? What if he had instead befriended Draco, made a first impression with him, and fallen into friendship with him? After befriending Ron and Hermione, the three new friends encounter Draco, who tries to get Potter to join up with his clique. Potter refuses, largely because he has already bonded with the friends Draco insulted.
So what would have happened if Harry met Draco on the train before Ron and Hermione? Would the Sorting Hat have still put Potter in Grffindor? Would Potter have been whispering "not Gryffindor" at the urging of Malfoy, and thus been swerved into Slytherin?
Is anything like this addressed in the books (I forget)? Is there later, further evidence that Harry would have ended up in Gryffindor no matter what, or was it his choice of friends before he got to Hogwarts that dictated where he ended up? Friends don't seem to get "split up" when the go to Hogwarts. The hat keeps them grouped together. And how gay am I?