LongestSubstring.py

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        left, maxSub, seen = 0, 0, set()
        for right in range(len(s)):
            while s[right] in seen:
                seen.remove(s[left])
                left += 1
            seen.add(s[right])
            maxSub = max(maxSub, (right - left) + 1)
        return maxSub