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