Life of Pi and The Catcher in the Rye both use first-person narration which gives the reader direct insight into what the character/narrator is thinking. The narrative structure of the two novels is very similar. Life of Pi also includes an authorial narration at the beginning - given from a vantage point after the events have taken place - and a transcript at the end. But in terms of style, Catcher is also divided into three similar narrations: the 32-year-old narrator, which may be Salinger himself looking back, the 17-year-old institutionalized Holden and then his journey when he was 16. We see Life of Pi through Pi's eyes and we see The Catcher in the Rye through Holden's eyes. This is important because both novels are about each boy's psychological development.
There are some similar themes. Both Holden and Pi feel alienated, albeit for different reasons. Pi has lost his family and must grow up immediately in order to survive. His only companion is a "Bengal tiger" who is both a friend and a predator. Interestingly, Richard Parker is also an adult figure so there is a connection here. Pi has an ambivalent feeling about adults, not just with Richard Parker but with adults in general. He doesn't understand why they can't appreciate more than one religion, why they are so closed-minded. Holden doesn't care for adults at all. He is so convinced that they are all phonies that he resists growing up on that principle. This is probably the biggest similarity in the two novels in that they are both about two characters who must grow up but are reluctant to do so.