JavaScript-Caesar密码

Question

它对正数有效，但对负数无效。（我还应该指出，我还没有想到如何处理空格，我只是想让它首先为单个单词工作，然后从那里开始，谢谢！）

任何正确方向的指针都将不胜感激。

Kata说明：

函数caesarCipher应该接受一个字符串和一个数字(n)，并返回一个应用了凯撒密码的新字符串。凯撒密码将每个明文字母替换为不同的字母，在字母表的上下固定的位置。N表示应该应用的字母表上下移位的数目。它可能是消极的，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);
  });
});

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，您正在进行映射：

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

但是num为负数。当你减去一个负数时，你所做的就是把它的绝对值相加。

相反，您应该做：

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

我知道你的解决方案正在进行中。你必须考虑到：

• 当您对j+num求和进行翻译时会发生什么，并且它超出了字母表的界限。如果num.
为负值，也会发生同样的情况
• 在问题的声明中，它声明caesarcipher应该只接受两个参数，但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：）