Part One (Beginning-Cargo Ship) :

Departs from the novel-

~the movie doesn't go into as much detail about Pi's religious beliefs

~adds a love interest for Pi

~doesn't go into detail about how Pi thought about zoos, that animals actually like to be in a zoo, if well kept

The Plot

Part Two (Cargo Ship-Rescue) :

Departs from the novel-

~Pi never can fully tame Richard Parker

~Pi and his family spend lots of time on the cargo ship before it sinks, unlike in the book

Stays faithful to the novel-

~Carnivorous island looks just like Pi described it in the book

Part Three (Rescue-End) :

Departs from the novel-

~Shows how he is telling the story afterward, telling it to an author

~You get to see Pi and his wife and children later in his life, after all of his hardships

Stays faithful to the novel-

~Pi tells the same two stories to the Japanese representatives