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Luhn algorithm

The Luhn algorithm or Luhn formula, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers.

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open System.Text.RegularExpressions
open System

let input = "378282246310005"

let digits = input |> Seq.filter System.Char.IsNumber |> Seq.map (string >> int)
if (digits |> Seq.length) <> 0 then
    let multiply i n = 
        match i % 2 with 
        | 1 when n < 5 -> n * 2 
        | 1 -> (n * 2) - 9 
        | _ -> n
    let sum = digits |> Seq.rev |> Seq.mapi multiply |> Seq.sum
    sum % 10 = 0   
else
    false

namespace System

namespace System.Text

namespace System.Text.RegularExpressions

val input : string

Full name: Script.input

val digits : seq<int>

Full name: Script.digits

module Seq

from Microsoft.FSharp.Collections

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

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

type Char =
  struct
    member CompareTo : value:obj -> int + 1 overload
    member Equals : obj:obj -> bool + 1 overload
    member GetHashCode : unit -> int
    member GetTypeCode : unit -> TypeCode
    member ToString : unit -> string + 1 overload
    static val MaxValue : char
    static val MinValue : char
    static member ConvertFromUtf32 : utf32:int -> string
    static member ConvertToUtf32 : highSurrogate:char * lowSurrogate:char -> int + 1 overload
    static member GetNumericValue : c:char -> float + 1 overload
    ...
  end

Full name: System.Char

Char.IsNumber(c: char) : bool
Char.IsNumber(s: string, index: int) : bool

val map : mapping:('T -> 'U) -> source:seq<'T> -> seq<'U>

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

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

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

--------------------
type string = String

Full name: Microsoft.FSharp.Core.string

Multiple items
val int : value:'T -> int (requires member op_Explicit)

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

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>

val length : source:seq<'T> -> int

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

val multiply : (int -> int -> int)

val i : int

val n : int

val sum : int

val rev : source:seq<'T> -> seq<'T>

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

val mapi : mapping:(int -> 'T -> 'U) -> source:seq<'T> -> seq<'U>

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

val sum : source:seq<'T> -> 'T (requires member ( + ) and member get_Zero)

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

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More information

Link:	http://fssnip.net/7Wo
Posted:	5 years ago
Author:	Marnee Dearman
Tags:	luhn