Caesar Cipher Helper

September 10th 2018

Caesar Cipher Helper

Write a class that, when given a string, will return an uppercase string with each letter shifted forward in the alphabet by however many spots the cipher was initialized to.

For example:

var c = new CaesarCipher(5); // creates a CipherHelper with a shift of five
c.encode('Codewars'); // returns 'HTIJBFWX'
c.decode('BFKKQJX'); // returns 'WAFFLES'

If something in the string is not in the alphabet (e.g. punctuation, spaces), simply leave it as is. The shift will always be in range of [1, 26].

생성자 함수가 있고, 이 생성자 객체의 프로토타입에 암호를 만들고 해독하는 메서드를 추가하는 문제입니다. 암호를 만들고 해석할 때, 알파벳순으로 인자로 전달받은 숫자만큼 이동시키면 됩니다.

var CaesarCipher = function(shift) {
  this.encode = function(str) {
    var strArr = str.toLocaleUpperCase().split('');
    strArr = strArr.map(function(cur) {
      var num = cur.charCodeAt();
      if (num >= 65 && num <= 90) {
        num += shift;
        return num > 90 ? (num -= 26) : num;
      } else {
        return num;
      }
    });

    return strArr.reduce(function(acc, cur) {
      return acc + String.fromCharCode(cur);
    }, '');
  };

  this.decode = function(str) {
    var strArr = str.toLocaleUpperCase().split('');
    strArr = strArr.map(function(cur) {
      var num = cur.charCodeAt();
      if (num >= 65 && num <= 90) {
        num -= shift;
        return num < 65 ? (num += 26) : num;
      } else {
        return num;
      }
    });

    return strArr.reduce(function(acc, cur) {
      return acc + String.fromCharCode(cur);
    }, '');
  };
};

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