Comments on: Project Euler in F# – Problem 25

By: 10 one-line solutions for project euler | united-coders.com

10 one-line solutions for project euler | united-coders.com — Wed, 29 Dec 2010 11:46:42 +0000

[...] found an one-liner on sharp.it in [...]

By: Joel

Joel — Tue, 23 Feb 2010 22:18:36 +0000

Here’s a one-liner version:

let euler25 = Seq.unfold (fun (n0, n1) -> Some(n0, (n1, n0 + n1))) (0I,1I) |> Seq.takeWhile ((>) (pown 10I 999)) |> Seq.length;;

By: claudio

claudio — Fri, 03 Oct 2008 21:38:49 +0000

You have to delete the second line, it was only required before the September CTP release.

By: Maxwell

Maxwell — Fri, 03 Oct 2008 18:15:52 +0000

When I try to paste any of your programs into Visual Studio 2008 with the September CTP of F# (1.9.6.2), I get the following error for line 2:

Error 1
The namespace ‘BigInt’ is not defined.
C:\Users\Owner\Documents\Visual Studio 2008\Projects\FSharp1\FSharp1\Program.fs
2
28
FSharp1Program.cs:

#light
open Microsoft.FSharp.Math.BigInt

let has1000Digits (n : Microsoft.FSharp.Math.BigInt) =
  n.ToString().Length = 1000

let euler25 =
  ((1I,1I) |> Seq.unfold
    (fun (n0, n1) ->
      (if has1000Digits n0 then None
        else Some(n0, (n1, n0 + n1))))
    |> Seq.length) + 1

By: Gavin

Gavin — Sat, 20 Sep 2008 02:10:14 +0000

A nicer way to check if a number has 1000 digits is:

let has1000Digits n =
   let oneThousandDigits = (BigInt.pow 10I 999I)
   n >= oneThousandDigits

with this change it runs considerably faster.