On Friday, 26 February 2016 at 08:05:09 UTC, Joseph Rushton
Wakeling wrote:
On Thursday, 25 February 2016 at 17:27:25 UTC, Andrei
Alexandrescu wrote:
So we have
https://dlang.org/phobos/std_random.html#.randomCover which
needs to awkwardly allocate memory to keep track of the
portions of the array already covered.
Yes, this is definitely a standout in terms of being an
unpleasant solution. It means that you require o(N) memory
even when you're dealing with a lazily-evaluated range -- it
would probably be more efficient in practice to just write the
input into an array and do an in-place shuffle. :-(
This could be fixed by devising a PRNG that takes a given
period n and generates all numbers in [0, n) in exactly n
steps.
However, I've had difficulty finding such PRNGs. Most want the
maximum period possible so they're not concerned with a given
period. Any insights?
I'll try to see what I can find. This must be something that
other lazy/functional communities (Haskell, Clojure, ...) have
had to contend with.
A few potential lines of exploration here:
http://apfelmus.nfshost.com/articles/random-permutations.html
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.150.9347&rep=rep1&type=pdf
