class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:

        # base case
        if not len(s):
            return 0

        hashset = set()

        left = 0; right = 0
        max_length = 0


        while(right < len(s)):

            if s[right] not in hashset:
                # keep adding the character untill we find duplicate
                hashset.add(s[right])
                max_length = max(max_length, right - left + 1)
                right += 1
            else:
                # once duplicate is found, keep removing elements from the left and update
                # the left pointer untill the repeating character is removed and we have
                # moved the left pointer to the next element of the duplicate character
                while(s[right] in hashset):
                    hashset.remove(s[left])
                    left += 1

                max_length = max(max_length, right - left + 1)

        return max_length