JavaScript -凯撒密码

Question

我知道过去有一些关于凯撒密码的帖子，我曾经看过，但是我没有找到一个帮助我解决这个问题的答案，因此我的帖子。

语言是JavaScript。我已经写了三个测试，其中两个已经通过了，但是第三个没有通过。我尝试使用嵌套的for循环循环遍历字母表和str，并对它们进行比较，然后根据数字上下移动字母索引，然后将字母推入一个新数组，并在最后返回已连接的数组。

它适用于正数，但不是负数。(我还应该指出，我还没有想过如何处理空间，我只想让它先用一个单词，然后从那里开始，谢谢！)

任何指向正确方向的指示都将不胜感激。

Kata指令：

函数caesarCipher应该接受一个字符串和一个数字(n)，并返回一个新字符串，并应用凯撒密码。凯撒密码用不同的字母替换每一个明文字母，这是字母上下固定的位置。N表示应应用字母表的上下移位数。可能是消极的，也可能是积极的。

  E.g.
  caesarCipher('hello', 2)
    --> 'jgnnq'
  caesarCipher('hello world!', -3)
    --> 'ebiil tloia!'

我的测试：

​

const caesarCipher = require("../katas/caesar-cipher");
const { expect } = require("chai");

describe.only("caesarCipher", () => {
  it("returns an empty string when passed an empty string", () => {
    const alphabet = [
      "a",
      "b",
      "c",
      "d",
      "e",
      "f",
      "g",
      "h",
      "i",
      "j",
      "k",
      "l",
      "m",
      "n",
      "o",
      "p",
      "q",
      "r",
      "s",
      "t",
      "u",
      "v",
      "w",
      "x",
      "y",
      "z"
    ];
    const str = "";
    const num = 2;
    const actualResults = caesarCipher(alphabet, str, num);
    const expectedResults = "";
    expect(actualResults).to.equal(expectedResults);
  });
  it("returns a string with the letters replaced by the number of shifts up the alphabet", () => {
    const alphabet = [
      "a",
      "b",
      "c",
      "d",
      "e",
      "f",
      "g",
      "h",
      "i",
      "j",
      "k",
      "l",
      "m",
      "n",
      "o",
      "p",
      "q",
      "r",
      "s",
      "t",
      "u",
      "v",
      "w",
      "x",
      "y",
      "z"
    ];
    const str = "hi";
    const num = 2;
    const actualResults = caesarCipher(alphabet, str, num);
    const expectedResults = "jk";
    expect(actualResults).to.equal(expectedResults);
  });
  it("returns a string with the letters replaced by the number of shifts down the alphabet", () => {
    const alphabet = [
      "a",
      "b",
      "c",
      "d",
      "e",
      "f",
      "g",
      "h",
      "i",
      "j",
      "k",
      "l",
      "m",
      "n",
      "o",
      "p",
      "q",
      "r",
      "s",
      "t",
      "u",
      "v",
      "w",
      "x",
      "y",
      "z"
    ];
    const str = "dog";
    const num = -3;
    const actualResults = caesarCipher(alphabet, str, num);
    const expectedResults = "ald";
    expect(actualResults).to.equal(expectedResults);
  });
});

​

我的解决方案：

​

function caesarCipher(alphabet, str, num) {
  const strToArray = str.split("");
  console.log(strToArray);
  const cipheredStr = [];
  for (let i = 0; i < strToArray.length; i++) {
    for (let j = 0; j < alphabet.length; j++) {
      if (strToArray[i] === alphabet[j] && Math.sign(num) === 1) {
        console.log(Math.sign(num));
        cipheredStr.push(alphabet[(j += num)]);
      } else if (strToArray[i] === alphabet[j] && Math.sign(num) === -1) {
        console.log(Math.sign(num));
        console.log(alphabet[(j -= num)]);
        cipheredStr.push(alphabet[(j -= num)]);
      }
    }
  }
  console.log(cipheredStr.join(""));
  return cipheredStr.join("");
}

​

结果：

​

caesarCipher
[]

    ✓ returns an empty string when passed an empty string
[ 'h', 'i' ]
1
1
jk
    ✓ returns a string with the letters replaced by the number of shifts up the alphabet
[ 'd', 'o', 'g' ]
-1
g
-1
r
-1
j
jum
    1) returns a string with the letters replaced by the number of shifts down the alphabet


  2 passing (15ms)
  1 failing

  1) caesarCipher
       returns a string with the letters replaced by the number of shifts down the alphabet:

      AssertionError: expected 'jum' to equal 'ald'
      + expected - actual

      -jum
      +ald
      
      at Context.<anonymous> (spec/caesar-cipher.spec.js:108:30)
      at processImmediate (internal/timers.js:456:21)

​

Answer 1

问题是，当num为负值时，您正在执行映射：

cipheredStr.push(alphabet[(j -= num)]);

但num为阴性。当你减去一个负数时，你所做的就是增加它的绝对值。

相反，你应该这样做：

cipheredStr.push(alphabet[j + num]);

另外，请注意，要计算字母表中的索引，不需要将=放在其中。

​

Side notes

​

我知道你的解决方案是一项正在进行的工作。你必须考虑到：

，

• ，当你把j + num和起来做翻译时，它超出了你的字母表的界限。同样的事情也可能发生在num.
• In的负值问题的声明中，它声明caesarCipher只能接受两个参数，但是您将字母表作为第一个参数传递！

祝您的代码好运，并继续尝试:)

Answer 2

let alphabets = 'abcdefghijklmnopqrstuvwxyz';
let arr = alphabets.split('')
// Cipher Get
function getCipher(str= alphabets, shift=3){
    return arr.reduce((a, c, i) => {
        let result = [...a]
        let tIndex = ( i + shift) % arr.length
        result[i]=arr[tIndex]
        return result;
    },[])
}

// Encrypt 
let stringToEnc = 'danger'
console.log('Plain Text -', stringToEnc)
let cipheredAlphabets = getCipher()
let encryptedStr = stringToEnc
    .toLowerCase()
    .split('')
    .map(function(p, i){
        let indexInAlphabets = arr.findIndex(c => p == c)
        return (cipheredAlphabets[indexInAlphabets])
    })
let encryptedText = encryptedStr.join('')
console.log('encrypted text - ', encryptedText)

// Decrypt
let cipherForDecrypt = getCipher(alphabets, -3)

let decryptedStr = encryptedText
    .toLowerCase()
    .split('')
    .map(function(p, i){
        let indexInAlphabets = cipheredAlphabets.findIndex(c => p == c)
        return (arr[indexInAlphabets])
    })
console.log('decrypted text - ', decryptedStr.join(''))