Naive factorial implementation

[Iaroslav Postovalov]

The current implementation of factorial has two problems:

1. It demonstrates literally nothing except the factorial's definition. To be meaningful it should contain some optimizations like prime factorization.
2. It uses Int, hence it is correct only in [ 0 .. 12 ] range.
   
   Even using ULong will allow values only from 0 to 20 inclusively, so only long arithmetic can have any practical value because for standard integer types the optimal algorithm is just to access array:

val factorials: ULongArray = ulongArrayOf(1uL, 1uL, 2uL ...)

[Dmitry Tsyvtsyn]

The Second problem has already been solved)
Look at here - https://github.com/KiberneticWorm/Kotlin-Algorithms-and-Design-Patterns/blob/master/src/main/kotlin/other/FactorialBigWithCache.kt

[Dmitry Tsyvtsyn]

Can you elaborate on the first point please?

[Iaroslav Postovalov]

Can you elaborate on the first point please?

Just google for "efficient factorial algorithm".

[Dmitry Tsyvtsyn]

Thanks) I'll do it

[Dmitry Tsyvtsyn]

I found more efficient algorithms for factorial, but I couldn't implement it.
Could you make a pull request?

[Dmitry Tsyvtsyn]

I implemented an efficient algorithm (from google guava library)
FactorialAdvanced