Caesars Cipher

JavaScript Algorithms and Data Structures Projects: Caesars CipherPassed


One of the simplest and most widely known ciphers is a Caesar cipher, also known as a shift cipher. In a shift cipher the meanings of the letters are shifted by some set amount.

A common modern use is the ROT13 cipher, where the values of the letters are shifted by 13 places. Thus 'A' ↔ 'N', 'B' ↔ 'O' and so on.

Write a function which takes a ROT13 encoded string as input and returns a decoded string.

All letters will be uppercase. Do not transform any non-alphabetic character (i.e. spaces, punctuation), but do pass them on.

const rot13 = str =>
  String.fromCharCode(...str.split('').map(l => 
    /\w/.test(l) ? 
      (l.charCodeAt(0) - 'A'.charCodeAt(0) + 13) % 26 + 'A'.charCodeAt(0)
    :
      l.charCodeAt(0)
  ));

[
    rot13("SERR PBQR PNZC") ,
    rot13("SERR CVMMN!") ,
    rot13("SERR YBIR?") ,
    rot13("GUR DHVPX OEBJA SBK WHZCF BIRE GUR YNML QBT.")
].forEach(result => console.log(result));

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