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Functional and simple version for Collatz Conjecture or 3n + 1 Problem

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//https://en.wikipedia.org/wiki/Collatz_conjecture
//https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=36

let min a b = if (a > b) then b else a
let max a b = if (b > a) then b else a
let f a b =
  let g j =
    seq { 
      let mutable i = j
      while (i > 1) do
        yield i
        i <- if ((i % 2) = 0) then i / 2 else 3 * i + 1
      yield 1
    }
  seq{(min a b)..(max a b)} |> Seq.map g
let max_length a b = f a b |> Seq.map  (fun x -> x |> Seq.length) |> Seq.max
let print_all a b  = f a b |> Seq.iter (fun x -> printfn "%A" (x |> Seq.toList))

(*

> print_all 1 10;;
[1]
[2; 1]
[3; 10; 5; 16; 8; 4; 2; 1]
[4; 2; 1]
[5; 16; 8; 4; 2; 1]
[6; 3; 10; 5; 16; 8; 4; 2; 1]
[7; 22; 11; 34; 17; 52; 26; 13; 40; 20; 10; 5; 16; 8; 4; 2; 1]
[8; 4; 2; 1]
[9; 28; 14; 7; 22; 11; 34; 17; 52; 26; 13; 40; 20; 10; 5; 16; 8; 4; 2; 1]

> max_length 1 10;;
val it : int = 20
> max_length 100 200;;
val it : int = 125
> max_length 201 210;;
val it : int = 89
> max_length 900 1000;;
val it : int = 174

*)

val min : a:'a -> b:'a -> 'a (requires comparison)

Full name: Script.min

val a : 'a (requires comparison)

val b : 'a (requires comparison)

val max : a:'a -> b:'a -> 'a (requires comparison)

Full name: Script.max

val f : a:int -> b:int -> seq<seq<int>>

Full name: Script.f

val a : int

val b : int

val g : (int -> seq<int>)

val j : int

Multiple items
val seq : sequence:seq<'T> -> seq<'T>

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

--------------------
type seq<'T> = System.Collections.Generic.IEnumerable<'T>

Full name: Microsoft.FSharp.Collections.seq<_>

val mutable i : int

module Seq

from Microsoft.FSharp.Collections

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

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

val max_length : a:int -> b:int -> int

Full name: Script.max_length

val x : seq<int>

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

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

val max : source:seq<'T> -> 'T (requires comparison)

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

val print_all : a:int -> b:int -> unit

Full name: Script.print_all

val iter : action:('T -> unit) -> source:seq<'T> -> unit

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

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

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

val toList : source:seq<'T> -> 'T list

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

Raw view Test code New version

More information

Link:	http://fssnip.net/7OI
Posted:	8 years ago
Author:	Fabio Galuppo
Tags:	functional , seq