public int lengthOfLongestSubstring(String s) {
        int maxLength = 0;
        HashMap<Character, Integer> map = new HashMap<>();
        for (int end = 0 , start = 0; end <s.length() ; end++) {
            char c = s.charAt(end);
            if (map.containsKey(c)){
                start = Math.max(start,map.get(c));
            }
            maxLength = Math.max(maxLength,end-start+1);
            map.put(c,end+1);
        }
        return maxLength;
    }