/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
  //遇到一个重复元素时，结束
  let max = 0;
  let countArr = [];
  let arr = s.split('');
  for (let i = 0; i < arr.length; i++) {
    countArr.push(arr[i]);
    //没结尾
    if (arr[i+1] != undefined) {
      //不包含下一个元素
      if (countArr.indexOf(arr[i+1]) < 0) {
        if (max < countArr.length) {
          max = countArr.length; 
        } 
      } 
      //包含下一个元素
      else {
        countArr.splice(0, countArr.indexOf(arr[i+1])+1);
        //console.log(countArr);
      }           
    } 
    //结束
    else {
      max++;
    }  
  }
  
  //console.log(max);
  return max;
};