class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        str_dic = {}
        i, ans = 0, 0
        for j in range(len(s)):
            if s[j] in str_dic:
                i = max(str_dic[s[j]], i)
            ans = max(ans, j-i+1)
            str_dic[s[j]] = j + 1
        return ans