Leetcode 3. Longest Substring Without Repeating Characters

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        maxLen = 0
        keep = []

        for i in range(len(s)):
            if s[i] in keep:
                maxLen = max(maxLen, len(keep))
                if s[i] == s[i-1]: keep = []
                else: keep = keep[keep.index(s[i])+1:]

            keep.append(s[i])
        return max(maxLen, len(keep))

https://leetcode.com/problems/longest-substring-without-repeating-characters/