var licenseKeyFormatting = function(s, k) {
    let newS=s.replace(/-/g,'')
    function replaceStr(str){
        let strArr=[...str]
        for(let i=0;i<strArr.length;i++){ 
            let asciiCode=strArr[i].charCodeAt(0)
            if(asciiCode>=97 && asciiCode<=122){
                strArr[i]=String.fromCharCode(asciiCode-32)
            }
        }
        return strArr.join('')
    }
    newS=replaceStr(newS)
    let result=''
    let headNum=newS.length%k
    headNum!==0?
    (newS.length<=k?result+=newS.slice(0,headNum):result+=newS.slice(0,headNum)+'-')
    :''
    for(let i=headNum+k;i<=newS.length;i+=k){
        result+=newS.slice(i-k,i)
        i!==newS.length?result+='-':''
    }
    return result
};

时间复杂度：O(n)，n为字符串长度
空间复杂度：O(1)，用到了额外常数个变量