alt-split.js

// Simple Encryption #1 - Alternating Split
// DESCRIPTION:
// Implement a pseudo-encryption algorithm which given a string S and an integer N concatenates all the odd-indexed characters of S with all the even-indexed characters of S, this process should be repeated N times.

// Examples:

// encrypt("012345", 1)  =>  "135024"
// encrypt("012345", 2)  =>  "135024"  ->  "304152"
// encrypt("012345", 3)  =>  "135024"  ->  "304152"  ->  "012345"

// encrypt("01234", 1)  =>  "13024"
// encrypt("01234", 2)  =>  "13024"  ->  "32104"
// encrypt("01234", 3)  =>  "13024"  ->  "32104"  ->  "20314"
// Together with the encryption function, you should also implement a decryption function which reverses the process.

// If the string S is an empty value or the integer N is not positive, return the first argument without changes.

function encrypt(text, n) {
    if(n <= 0 || !text){
      return text
    }
    let odd = text.split("").filter((elem,i) => i % 2 ===1)
    let even = text.split("").filter((elem,i) => i % 2 === 0)
    return encrypt(odd.concat(even).join(""), n-1)
  }
  
  function decrypt(encryptedText, n) {
    if(n <= 0|| !encryptedText){
      return encryptedText
    }
    let splitNum =  encryptedText.length/2
    let odd = encryptedText.slice(0,splitNum)
    let even = encryptedText.slice(splitNum)
    let newText = []
    for(let i = 0; i < encryptedText.length; i++){
      if(i % 2 === i-1){
        newText.push(odd[i])
        newText.push(even[i])
      }else{
        newText.push(even[i])
        newText.push(odd[i])
      }
    }
    return decrypt(newText.join(""), n-1)
  }