Can you suggest me books in the style of Terry Pratchett or Douglas Adams?

Jack Handey's short stuff is probably his most famous work, but he also wrote a novel called The Stench of Honolulu.

John Swartzwelder is another comedy legend, he wrote nearly 60 episodes of The Simpsons, and he has a series of detective-pastiche novels (maybe novellas), starting with The Time Machine Did It.

I like these books and think they're along the same lines as Pratchett and Adams, but they are distinctly sillier.