3. Longest Substring Without Repeating Characters

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        sub=''
        longest=''
        for i in s:
            if i not in sub:
                sub+=i
            else:
                if len(sub)>=len(longest):
                    longest=sub
                sub=sub[sub.find(i)+1:]+i
        return max(len(longest),len(sub))