Comments on: Project Euler in F# – Problem 28

By: ggse

ggse — Wed, 15 Jul 2009 11:52:22 +0000

The sum is also given by a formula : for a n by n spiral, S = (4*n^3+3*n^2+8*n-9)/6.

By: claudio

claudio — Mon, 25 May 2009 07:29:38 +0000

Jorge and Thedric, you both guessed it right!

The solution with fold is perfect while the recursive one is easier to understand and to use with academic purposes.

By: Jorge Esquer

Jorge Esquer — Sat, 23 May 2009 23:30:58 +0000

Here’s my take with fold:

printf “%A” (Seq.fold (fun sum x -> sum + 4 * x * x – 6 * (x – 1)) 1 [3..2..1001])

By: Thedric Walker

Thedric Walker — Sat, 23 May 2009 16:37:47 +0000

Pretty cool article. If I had to guess, I would say putting in any even number would cause this to blow up. This is because the exit condition assumes that n-2 will eventually result in 1. However, for even numbers that never happens.

But that’s just my guess.

By: Jorge Esquer

Jorge Esquer — Sat, 23 May 2009 04:38:48 +0000

Would the bug be that, if you pass an even number as n, it’ll never match 1 because it will jump from 2 to 0 and thus keep subtracting 2 indefinitely?