How to resolve the algorithm Rot-13 step by step in the Julia programming language

Published on 22 June 2024 08:30 PM
#Julia

How to resolve the algorithm Rot-13 step by step in the Julia programming language

Table of Contents

Problem Statement

Implement a   rot-13   function   (or procedure, class, subroutine, or other "callable" object as appropriate to your programming environment). Optionally wrap this function in a utility program   (like tr,   which acts like a common UNIX utility, performing a line-by-line rot-13 encoding of every line of input contained in each file listed on its command line,   or (if no filenames are passed thereon) acting as a filter on its   "standard input."

(A number of UNIX scripting languages and utilities, such as   awk   and   sed   either default to processing files in this way or have command line switches or modules to easily implement these wrapper semantics, e.g.,   Perl   and   Python). The   rot-13   encoding is commonly known from the early days of Usenet "Netnews" as a way of obfuscating text to prevent casual reading of   spoiler   or potentially offensive material. Many news reader and mail user agent programs have built-in rot-13 encoder/decoders or have the ability to feed a message through any external utility script for performing this (or other) actions. The definition of the rot-13 function is to simply replace every letter of the ASCII alphabet with the letter which is "rotated" 13 characters "around" the 26 letter alphabet from its normal cardinal position   (wrapping around from   z   to   a   as necessary). Thus the letters   abc   become   nop   and so on. Technically rot-13 is a   "mono-alphabetic substitution cipher"   with a trivial   "key". A proper implementation should work on upper and lower case letters, preserve case, and pass all non-alphabetic characters in the input stream through without alteration.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Rot-13 step by step in the Julia programming language

The provided Julia code performs the following tasks:

1. rot13 Function:

  • This function takes a single character, c, as input.
  • It checks if the character is lowercase using islowercase(c); if it is, it sets shft to 'a'. Otherwise, it sets shft to 'A', indicating uppercase.
  • It checks if the character is a letter (A-Z or a-z) using isletter(c).
  • If it's a letter, it rotates it by 13 positions in the alphabet, either forwards or backward, depending on whether it's uppercase or lowercase. This is achieved using the modulo operation (%) and some arithmetic.
  • If the character is not a letter, it's left unchanged.

2. Applying rot13 to a String:

  • This part creates a new function that takes an abstract string, str, as input.
  • It uses the map function to apply the rot13 function to each character in the string.
  • The result is a new string with all its letters rotated by 13 positions in the alphabet.

3. Replacing Characters Using a Custom Function:

  • This line uses the replace function to replace all characters in the string "nowhere ABJURER" that match the regular expression [A-Za-z] (all letters) with a new string.
  • The new string is computed using the inner function s -> map(c -> c + (uppercase(c) < 'N' ? 13 : -13), s).
  • This function takes a string s as input and maps a new function over each character in s. The new function checks if the character is uppercase or lowercase by comparing it to 'N' (the middle of the alphabet). If it's uppercase, it moves it backward by 13 positions in the alphabet, and if it's lowercase, it moves it forward by 13 positions.
  • The result is that the replaced characters in the original string are shifted by 13 positions in the alphabet, either forwards or backward, depending on their case.

Source code in the julia programming language

# Julia 1.0
function rot13(c::Char)
    shft = islowercase(c) ? 'a' : 'A'
    isletter(c) ? c = shft + (c - shft + 13) % 26 : c
end

rot13(str::AbstractString) = map(rot13, str)


replace("nowhere ABJURER", r"[A-Za-z]" => s -> map(c -> c + (uppercase(c) < 'N' ? 13 : -13), s))

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