CODEWITHSUNDEEP
f#
Maller94
Maller94

Reputation: 33

Applying function repeatedly to generate List

enter image description here

I currently have this f# function

let collatz' n =
match n with
| n when n <= 0 -> failwith "collatz' :n is zero or less"
| n when even n = true -> n / 2
| n when even n = false -> 3 * n + 1

Any tips for solving the following problem in F#?

Upvotes: 0

Views: 104

Answers (1)

Flippie van Dyk
Flippie van Dyk

Reputation: 69

As said in the comments, you need to give a bit more information for any really specific advice, but based on what you have I'll add the following.

The function you have declared satisfies the definition of the Collatz function i.e. even numbers -> n/2 ,and odd number -> 3n + 1.

So really you only need applyN, let's break it down into its pieces


( `a -> `a) -> `a -> int -> `a list
applyN f n N

That definition is showing you exactly what the function expects.

lets look at f through to N

f -> a function that takes some value of type 'a (in your case likely int) and produces a new value of type 'a. This corresponds to the function you have already written collatz`

n -> is your seed value. I don't think elaboration is required.

N -> This looks like a maximum amount of steps to go through. In the example posted, if N was larger, you would see a loop [ 1 ;4; 2; 1; 4... ] and if it was smaller it would stop sooner.

So that is what the function takes and need to do, so how can we achieve this?

I would suggest making use of scan.

The scan function is much like fold, but it returns each interim state in a list. Another option would be making use of Seq.unfold and then only taking the first few values.

Now, I could continue and give some source code, but I think you should try yourself for now.

Upvotes: 2

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