lengthOfLongestSubstring.py

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        start = end = 0
        current_chars = set()
        length = max_length = 0
        while end < len(s):
            if s[end] not in current_chars:
                current_chars.add(s[end])
                length += 1
                if length > max_length:
                    max_length = length
                end += 1
            else:
                while start < end:
                    current_chars.remove(s[start])
                    length -= 1
                    start += 1
                    if s[start - 1] == s[end]:
                        break

        return max_length