请从字符串中找出一个最长的不包含重复字符的子字符串，计算该最长子字符串的长度。

 

 

 s.length <= 40000

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int res = 0;
        Set<Character> set = new HashSet<>();
        for(int l = 0, r = 0; r < s.length(); r++)
        {
            char c = s.charAt(r);
            while (set.contains(c)){
                set.remove(s.charAt(l++));
            }
            set.add(c);
            res = Math.max(res, r - l + 1);
        }
        return res;
    }
}