func lengthOfLongestSubstring(_ s: String) -> Int {
        if s.count == 0 {
            return 0;
        }
        
        var map = [String: Int]();
        var maxs = 0;
        var left = 0;
        let stringArray = s.map{ $0 };
        
        for (i, sub) in stringArray.enumerated() {
            if map.keys.contains(String(sub)) {
                left = max(left, (map[String(sub)]! + 1));
            }
            map.updateValue(i, forKey: String(sub));
            maxs = max(maxs, i - left + 1);
        }
        return maxs;
    }