JS 算法

1、js 统计一个字符串出现频率最高的字母/数字

  let str = 'absafdaf234234323232'

      let a = [...str]
    //   alert(a instanceof Array)
    const strChar = str => {
      let strArr = [...str]
      maxValue='',
      maxKey = ''
      obj = {}

      strArr.forEach(val =>{
        obj[val] = obj.hasOwnProperty(val) ? obj[val]+1 : 1
        if(obj[val] > maxValue){
            maxValue = obj[val]
            maxKey = val
        }
      })
      return {
        key: maxKey,
        value: maxValue
      }
    }

    console.log(strChar(str))  // {key: 3, value: 5}

2、数组去重

forEach

let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
    let obj = {}
    arr.forEach(value => {
      // 对象key值是唯一， 使用  Object.keys 转为数组形式
        obj[value] = 0
    })
    return Object.keys(obj)
}
console.log(unique(arr))  // ['1','2','3','a','b']

filter

  let arr = [1,2,2,2,5,3,4,5,1]
   const unique = arr => {
     return  arr.filter((ele,index, array) =>{
        return index === array.indexOf(ele)
      })
   }
  let v =  unique(arr)
  console.log(v)

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']

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']

3、翻转字符串

let str ="Hello Dog";
const reverseString = str =>{
    return [...str].reverse().join("");
}
console.log(reverseString(str))   // goD olleH

数组中最大差值

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

冒泡