手撕JS高手进阶（持续更新中…）

关于实现js中一些常见的方法属于面试中的常问问题，可能刚开始接触的时候会一筹莫展。知道和理解其中的原理能够在日常开发中更如鱼得水，面对面试也不成问题。

另外，学会以目的（实现的功能）为导向一层一层反推，总结出实现的思路就能按照步骤直接实现或者曲线实现（整理不易记得点赞哈）。

1. 实现一个函数，返回一个数组中最大值和最小值

function maxAndMin(array) {
  if (array.length === 0) {
    return { max: null, min: null };
  }

  let max = array[0];
  let min = array[0];

  for (let i = 1; i < array.length; i++) {
    if (array[i] > max) {
      max = array[i];
    }
    if (array[i] < min) {
      min = array[i];
    }
  }

  return { max, min };
}

const array1 = [1, 2, 3, 4, 5];
const result1 = maxAndMin(array1);
console.log(result1); // { max: 5, min: 1 }

const array2 = [10, 5, 20, 15, 30];
const result2 = maxAndMin(array2);
console.log(result2); // { max: 30, min: 5 }

2. 实现一个函数，判断一个字符串是否是回文

function isPalindrome(string) {
  if (string.length === 0) {
    return true;
  }

  string = string.toLowerCase().replace(/[^a-zA-Z0-9]/g, "");

  const reversedString = string.split("").reverse().join("");

  return string === reversedString;
}

const string1 = "racecar";
const result1 = isPalindrome(string1);
console.log(result1); // true

const string2 = "hello world";
const result2 = isPalindrome(string2);
console.log(result2); // false

3. 实现一个函数，计算两个日期之间的天数

function daysBetween(date1, date2) {
  const oneDay = 1000 * 60 * 60 * 24;

  const difference = Math.abs(date1 - date2);

  return Math.ceil(difference / oneDay);
}

const date1 = new Date("2023-03-08");
const date2 = new Date("2023-03-15");
const result1 = daysBetween(date1, date2);
console.log(result1); // 7

const date3 = new Date("2023-03-08");
const date4 = new Date("2023-04-08");
const result2 = daysBetween(date3, date4);
console.log(result2); // 31

4. 实现一个函数，打乱一个数组

function shuffleArray(array) {
  for (let i = array.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [array[i], array[j]] = [array[j], array[i]];
  }

  return array;
}

const array1 = [1, 2, 3, 4, 5];
const result1 = shuffleArray(array1);
console.log(result1); // [4, 1, 5, 2, 3]

const array2 = [10, 5, 20, 15, 30];
const result2 = shuffleArray(array2);
console.log(result2); // [30, 10, 5, 15, 20]

5. 实现一个函数，将一个整数转换为罗马数字

function intToRoman(num) {
  const romanNumerals = {
    1: "I",
    4: "IV",
    5: "V",
    9: "IX",
    10: "X",
    40: "XL",
    50: "L",
    90: "XC",
    100: "C",
    400: "CD",
    500: "D",
    900: "CM",
    1000: "M",
  };

  let result = "";

  for (const value in romanNumerals) {
    while (num >= value) {
      result += romanNumerals[value];
      num -= value;
    }
  }

  return result;
}

const num1 = 3;
const result1 = intToRoman(num1);
console.log(result1); // "III"

const num2 = 4;
const result2 = intToRoman(num2);
console.log(result2); // "IV"

const num3 = 9;
const result3 = intToRoman(num3);
console.log(result3); // "IX"

const num4 = 49;
const result4 = intToRoman(num4);
console.log(result4); // "XLIX"

const num5 = 1990;
const result5 = intToRoman(num5);
console.log(result5); // "MCMXC"

6. 实现一个函数，将一个罗马数字转换为整数

function romanToInt(roman) {
  const romanNumerals = {
    I: 1,
    V: 5,
    X: 10,
    L: 50,
    C: 100,
    D: 500,
    M: 1000,
  };

  let result = 0;
  let previousValue = 0;

  for (let i = roman.length - 1; i >= 0; i--) {
    const currentValue = romanNumerals[roman[i]];

    if (currentValue < previousValue) {
      result -= currentValue;
    } else {
      result += currentValue;
    }

    previousValue = currentValue;
  }

  return result;
}

const roman1 = "III";
const result1 = romanToInt(roman1);
console.log(result1); // 3

const roman2 = "IV";
const result2 = romanToInt(roman2);
console.log(result2); // 4

const roman3 = "IX";
const result3 = romanToInt(roman3);
console.log(result3); // 9

const roman4 = "XLIX";
const result4 = romanToInt(roman4);
console.log(result4); // 49

const roman5 = "MCMXC";
const result5 = romanToInt(roman5);
console.log(result5); // 1990

7. 实现一个函数，判断一个数组是否包含重复元素

function containsDuplicates(array) {
  const set = new Set();

  for (let i = 0; i < array.length; i++) {
    if (set.has(array[i])) {
      return true;
    } else {
      set.add(array[i]);
    }
  }

  return false;
}

const array1 = [1, 2, 3, 4, 5];
const result1 = containsDuplicates(array1);
console.log(result1); // false

const array2 = [1, 2, 3, 4, 1];
const result2 = containsDuplicates(array2);
console.log(result2); // true

const array3 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1];
const result3 = containsDuplicates(array3);
console.log(result3); // true