public int lengthOfLongestSubstring(String s) {
        Map<Character,Integer> window=new HashMap<>();
        int left=0,right=0;
        int length=0;
        while(right<s.length())
        {
            char r=s.charAt(right);
            right++;
            window.put(r,window.getOrDefault(r,0)+1);
            while(window.get(r)>1)
            {
                char d=s.charAt(left);
                left++;
                window.replace(d,window.get(d)-1);    
            }
            length=Math.max(length,right-left);
        }

        return length;

    }