Algorithm-Caesars-Cipher.md

Problem Explanation:

• You need to write a function, which will take string encoded with Caesar cipher as a parameter and decode it.
• The one used here is ROT13 where the value of the letter is shifted by 13 places. e.g. 'A' ↔ 'N', 'T' ↔ 'G'.
• You have to shift it back 13 positions, such that 'N' ↔ 'A'.

Hint: 1

Use String.charCodeAt() to convert the English character to ASCII.

Hint: 2

Use String.fromCharCode() to convert ASCII to English character.

Hint: 3

Leave anything that doesn't come between A-Z as it is.

Spoiler Alert!

Solution ahead!

Code Solution:

First solution

function rot13(str) {
    var nstr="";
    for(var i=0; i<str.length; i++){
        //Checks if character lies between A-Z
        if(str.charCodeAt(i) < 65 || str.charCodeAt(i) > 91) {
            nstr += String.fromCharCode(str.charCodeAt(i));
            continue;
        }
        //N = ASCII 78, if the character code is less than 78, shift forward 13 places
        if(str.charCodeAt(i) < 78){
            nstr += String.fromCharCode(str.charCodeAt(i) + 13);
        }
        else{
            //Otherwise shift the character 13 places backward
            nstr += String.fromCharCode(str.charCodeAt(i) - 13);

        }
    }

    return nstr;
}

Second solution (advanced)

function rot13(str) {
  // Split str into a character array
  return str.split('')
  // Iterate over each character in the array
    .map.call(str, function(char) {
      // Convert char to a character code
      x = char.charCodeAt(0);
      // Checks if character lies between A-Z
      if (x < 65 || x > 91) {
        return String.fromCharCode(x);  // Return un-converted character
      }
      //N = ASCII 78, if the character code is less than 78, shift forward 13 places
      else if (x < 78) {
        return String.fromCharCode(x + 13);
      }
      // Otherwise shift the character 13 places backward
      return String.fromCharCode(x - 13);
    }).join('');  // Rejoin the array into a string
}

Code Explanation:

First solution

• A string variable nstr is declared and initialized to store the decoded string.
• The for loop is used to loop through each character of the input string.
• If the character is not uppercase English alphabets(i.e. its ascii doesn't lie between 65 and 91 ), we'll leave it as it is and continue with next iteration.
• If it's the uppercase English alphabet, we'll subtract 13 from it's ascii code.
• If the ascii code is less than 78, it'll get out of range when subtracted by 13 so we'll add 26(number of letters in English alphabets) to it so that after A it'll go back to Z. e.g. M(77) ↔ 77-13 = 64(Not an English alphabet) +26 = 90 ↔ Z(90)

Credits:

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