無重複字元的最長子串

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