public/subjects/scytale_decoder

scytale_cipher

Instructions

Create a function which decode a scytale cipher (also known as spartan cipher).

In practice, it is represented by a strip wrapped around a cylinder. The message is written across the loops of the strip (not along the strip). The message becomes coded if the radius of the cylinder changes, or the strip is removed from the cylinder.

Your function will receive a String representing the ciphered message, and a u32 representing the number of letters by turn of the strip around the cylinder.

If the ciphered message is empty or the letters per turn are 0 the function will return None.

Example

letters_per_turn 2: "scytale Code" -> "sec yCtoadle"

--------------------------------
  |s|  |c|  |y|  |t|  |a|  |l|
  |e|  | |  |C|  |o|  |d|  |e|
--------------------------------

letters_per_turn 4: "scytale Code" -> "steoca dylCe"

------------------------------------------
  |s|  |c|  |y|
  |t|  |a|  |l|
  |e|  | |  |C|
  |o|  |d|  |e|
------------------------------------------

Expected Functions

pub fn scytale_decoder(s: String, letters_per_turn: u32) -> Option<String> {
}

Usage

Here is a program to test your function

fn main() {
    println!("\"sec yCtoadle\" size=2 -> {:?}",
        scytale_decoder("sec yCtoadle".to_string(), 2));

    println!("\"steoca dylCe\" size=4 -> {:?}",
        scytale_decoder("steoca dylCe".to_string(), 4));
}

And its output

$ cargo run
"sec yCtoadle" size=2 -> Some("scytale Code")
"steoca dylCe" size=4 -> Some("scytale Code")
$