def lengthOfLongestSubstring(s):
    used = {}
    maxl = left = 0
    for i in range(len(s)):
        if s[i] in used and left <= used[s[i]]:
            left = used[s[i]]+1
        else:
            maxl = max(maxl, i - left + 1)
        used[s[i]] = i

    return maxl