[CodeWars] Alphabet Cipher

cipher.md

간단한 암/복호화

message: my secret code i want to secure
key:     passwordpasswordpasswordpasswor

var alphabet = 'abcdefghijklmnopqrstuvwxyz';
var key = 'password';

// creates a cipher helper with each letter substituted
// by the corresponding character in the key
var c = new VigenèreCipher(key, alphabet);

c.encode('codewars'); // returns 'rovwsoiv'
c.decode('laxxhsj'); // returns 'waffles'

키값을 받아서 키값+평문값 단 알파벳에 포함안된녀석을 그대로 출력(abc변수)

My Solution

function VigenèreCipher(key, abc) {
  var repeatpw = (s)=> s.split('').map((_,i)=>key[i%key.length]);
  var convert = (str, f)=> repeatpw(str).map(f).join('');

  this.encode = function (str) {
    return convert(str, (p,i)=> abc.indexOf(str[i])>=0? abc[(abc.indexOf(p)+abc.indexOf(str[i]))%abc.length] : str[i]);
  };
  this.decode = function (str) {
    return convert(str, (p,i)=> abc.indexOf(str[i])>=0? abc[(abc.length-abc.indexOf(p)+abc.indexOf(str[i]))%abc.length] : str[i]);
  };
}

제일 위에있던 베스트는 겁나게..긴데;;; 이것보단, 좀 내려가서 찾은 답이 훨 나은듯

Best Practice

function VigenèreCipher(key, alphabet) {
  function encode(direction, inStr) {
    var inChar, inIdx, outIdx, outChar, keyChar, offset;
    
    var outStr = '';
    
    // Process each character of the input string sequentially
    for (var pos = 0; pos < inStr.length; ++pos) {
      
      // Look up input character in the alphabet
      inChar = inStr.charAt(pos);
      inIdx = alphabet.indexOf(inChar);
      
      // If character isn't in alphabet, just copy it to output
      if (inIdx < 0)
        outChar = inChar;
      else {
        // Get the key character for the current position
        // and determine the shift distance
        keyChar = key.charAt(pos % key.length);
        offset = alphabet.indexOf(keyChar);
        
        // Shift the character forwards or backwards in
        // the alphabet, wrapping around if necessary
        outIdx = inIdx + direction * offset;
        if (outIdx >= alphabet.length)
          outIdx = outIdx - alphabet.length;
        else if (outIdx < 0)
          outIdx = outIdx + alphabet.length;
        
        outChar = alphabet.charAt(outIdx);
      }
      
      outStr += outChar;
    }
    
    return outStr;
  }

  // Encode by shifting characters forward in the alphabet
  this.encode = function(string) {
    return encode(1, string);
  };
  
  // Decode by shifting characters backwards in the alphabet
  this.decode = function(string) {
    return encode(-1, string);
  };
}

function VigenèreCipher(key, abc) {
  this.encode = (str) => encode(1, str);
  this.decode = (str) => encode(-1, str);
  function encode (mult, str) {
    return str.split('').map(function (letter, index) {
      var i = abc.indexOf(letter);
      return i < 0 ? letter : abc[(abc.length + i + abc.indexOf(key[index % key.length]) * mult) % abc.length];
    }).join('');
  }
}