0003. Longest Substring Without Repeating Characters.java

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