Was this based on a true story or just a work of fiction?
It's a science fiction story. Not based on any true story of any sort.
I've read both the original short story
Flowers for Algernon and the novel version
Charly.
I have to say that I think the original short story is more powerful and a stronger piece. The motif which the author uses in the short story (the entire short story is told through journal entries) works better in the short story.
Not only that, but I found the novel to be more depressing, and it made me dislike the character of Charlie more throughout the novel because of the subsequent choices Charlie makes with his girlfriend.
However, both are interesting stories. I definitely recommend
Flowers, but I would only check out
Charly if you really liked
Flowers.
I also wasn't a huge fan of the movie version, also called
Charly, because I thought it suffered from too much influence of the 60's. There's a random drugged out episode in the movie that I thought was unneeded, as well as the "makeup" scene between Charley and his girlfriend, which I thought was weak.