Longest Substring Without Repeating Characters

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int max = 0;
        
        
        if (s == null || s.length() == 0) {
            return 0;
        }
        
        HashSet<Character> hs = new HashSet<Character>();
        int left = 0;
        
        for (int i = 0; i < s.length(); i++) {
            if (!hs.contains(s.charAt(i))) {
                hs.add(s.charAt(i));
                max = Math.max(max, i - left + 1);
            } else {
                while (left < i && s.charAt(left) != s.charAt(i)) {
                    hs.remove(s.charAt(left));
                    left++;
                }
                left++;
            }
        }
        return max;
    }
}