3.无重复字符的最长字串

//用滑动窗口来做 
var lengthOfLongestSubstring = function(s) {
   let arr = [];
   let sArr = s.split('');
   let max = 0;
   sArr.forEach((item) => {
       while(arr.indexOf(item)!=-1) {
           arr.shift();
       }
       arr.push(item);
       max = Math.max(max, arr.length);
   })
   return max;

};