What is the titolo of this book?

I can't remember the main character's name. I keep thinking McGuire o McGee...

It's about a boy who has no parents. He meets a girl who carries aroun libri in a suitcase. She gives him the A encyclopedia to read. He ends up staying at her house, sleeping on the floor, I think. I alwo recall him sneaking out to sleep in the zoo. I remember there was a bully names Mars Bar and they all played "War"
There was a great race barrier... Blavk people lived on one side of the town, and white people on the other. there was a pizza negozio in the middle with a huge ball of knotted twine hanging in the drorway. Whoever untied it won a lifetime supply of pizza?

I can't remember anymore... I believe they turned this book into a Nickelodeon movie a few years back.