1、js 统计一个字符串出现频率最高的字母/数字
let str = 'asdfghjklaqwertyuiopiaia';const strChar = str => { let string = [...str], maxValue = '', obj = {}, max = 0; string.forEach(value => { obj[value] = obj[value] == undefined ? 1 : obj[value] + 1 if (obj[value] > max) { max = obj[value] maxValue = value } })return maxValue;}console.log(strChar(str)) // a复制代码 2、数组去重
2.1、forEach
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']const unique = arr => { let obj = {} arr.forEach(value => { obj[value] = 0 }) return Object.keys(obj)}console.log(unique(arr)) // ['1','2','3','a','b']复制代码 2.2、filter
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']const unique = arr => { return arr.filter((ele, index, array) => { return index === array.indexOf(ele) })}console.log(unique(arr)) // ['1','2','3','a','b']复制代码 2.3、set
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']const unique = arr => { return [...new Set(arr)]}console.log(unique(arr)) // ['1','2','3','a','b']复制代码 2.4、reduce
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']const unique = arr.reduce((map, item) => { map[item] = 0 return map}, {})console.log(Object.keys(unique)) // ['1','2','3','a','b']复制代码 3、翻转字符串
let str ="Hello Dog";const reverseString = str =>{ return [...str].reverse().join("");}console.log(reverseString(str)) // goD olleH复制代码 4、数组中最大差值
4.1、forEach
let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];const difference = arr => { let min = arr[0], max = 0; arr.forEach(value => { if (value < min) min = value if (value > max) max = value }) return max - min ;}console.log(difference(arr)) // 74复制代码 4.2、max、min
let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];const difference = arr => { let max = Math.max(...arr), min = Math.min(...arr); return max - min ;}console.log(difference(arr)) // 74复制代码 5、不借助临时变量，进行两个整数的交换
5.1、数组解构
let a = 2, b = 3; [b,a] = [a,b] console.log(a,b) // 3 2复制代码
5.2、算术运算（加减）
输入a = 2,b = 3,输出 a = 3,b = 2
let a = 2, b = 3;const swop = (a, b) => { b = b - a; a = a + b; b = a - b; return [a,b];}console.log(swop(2,3)) // [3,2]复制代码 5.3、逻辑运算（异或）
let a = 2, b = 3;const swop = (a, b) => { a ^= b; //x先存x和y两者的信息 b ^= a; //保持x不变，利用x异或反转y的原始值使其等于x的原始值 a ^= b; //保持y不变，利用x异或反转y的原始值使其等于y的原始值 return [a,b];}console.log(swop(2,3)) // [3,2]复制代码 6、排序 (从小到大)
6.1、冒泡排序
let arr = [43, 32, 1, 5, 9, 22];const sort = arr => { let res = [] arr.forEach((v, i) => { for (let j = i + 1; j < arr.length; j++) { if (arr[i] > arr[j]) { [arr[i],arr[j]] = [arr[j],arr[i]] } } }) return arr}console.log(sort(arr)) // [1, 5, 9, 22, 32, 43]复制代码