1. var replaceSpace = function(s) {
    2.     let arr = s.split('') 
    3.     let count = 0 //计数空格
    4.     arr.forEach(item => {
    5.         if(item===' '){
    6.             count++
    7.         }
    8.     })
    9.     let newArr = []
    10.     newArr.length = arr.length+count*2
    11.     for(let i=s.length-1,j=newArr.length-1;i>=0;i--,j--){
    12.         if(s[i]===' ') {
    13.             newArr[j] = 0
    14.             newArr[j-1] = 2
    15.             newArr[j-2] = '%'
    16.             j-=2
    17.         }else{
    18.             newArr[j] = s[i]
    19.         }
    20.     }
    21.     return newArr.join('')
    22. };