Largest Palindrome Number from Product of Two Three Digit Numbers

Here is an improved version twice shorter, than original

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//largest palindrone number made from product of two 3-digit numbers

let reverse (s:string) = new string(s |> Seq.toArray |> Array.rev)

let isPalindrone (x,y) =
  let s = string(x*y)
  s = reverse(s) 

let calculateSequence = Seq.unfold (fun (x,y) ->
  if(isPalindrone (x,y)) then
    Some((x,y), (x,(y-1)))
  else if(x=100 && y=100) then
    None
  else if(y=100) then
    Some((0,0), ((x-1),(x-1)))
  else
    Some((0,0), (x,(y-1)))) (999,999)
  

let max = 
  calculateSequence
  |> Seq.filter (fun x -> x>(1,1)) 
  |> Seq.maxBy (fun e -> fst(e)*snd(e))  

printfn "%A" max

val reverse : s:string -> string

Full name: Script.reverse

val s : string

Multiple items
val string : value:'T -> string

Full name: Microsoft.FSharp.Core.Operators.string

--------------------
type string = System.String

Full name: Microsoft.FSharp.Core.string

module Seq

from Microsoft.FSharp.Collections

val toArray : source:seq<'T> -> 'T []

Full name: Microsoft.FSharp.Collections.Seq.toArray

module Array

from Microsoft.FSharp.Collections

val rev : array:'T [] -> 'T []

Full name: Microsoft.FSharp.Collections.Array.rev

val isPalindrone : x:int * y:int -> bool

Full name: Script.isPalindrone

val x : int

val y : int

val calculateSequence : seq<int * int>

Full name: Script.calculateSequence

val unfold : generator:('State -> ('T * 'State) option) -> state:'State -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.unfold

union case Option.Some: Value: 'T -> Option<'T>

union case Option.None: Option<'T>

val max : int * int

Full name: Script.max

val filter : predicate:('T -> bool) -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.filter

val x : int * int

val maxBy : projection:('T -> 'U) -> source:seq<'T> -> 'T (requires comparison)

Full name: Microsoft.FSharp.Collections.Seq.maxBy

val e : int * int

val fst : tuple:('T1 * 'T2) -> 'T1

Full name: Microsoft.FSharp.Core.Operators.fst

val snd : tuple:('T1 * 'T2) -> 'T2

Full name: Microsoft.FSharp.Core.Operators.snd

val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

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More information

Link:	http://fssnip.net/12
Posted:	14 years ago
Author:	Nick Canzoneri
Tags:	sequence , project euler problem