Longest Substring Without Repeating Characters

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

        """
        At each step, right pointer points to a locations where we
        are trying to calculate length of longest string ending there.
        When we are iterating over the character corresponding to right pointer,
        we might have added one of the duplicate characters already in the hashset
        so we havwe to remove characters from left untill duplicate of s[right] is removed

        Think of it this way:
        how will you calcuate the longest substring ending at aright pointer
        """

        left = 0
        right = 0
        hashmap = {}
        longestsubstring = 0

        while left < len(s) and right < len(s):
            if s[right] in hashmap:
                del hashmap[s[left]]
                left += 1
            else:
                hashmap[s[right]] = right
                longestsubstring = max(longestsubstring, right-left+1)
                right += 1

        return longestsubstring

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

        left = 0
        right = 0
        # previously occured index stored here
        hashmap = {}
        longestsubstring = 0

        while left < len(s) and right < len(s):
            if s[right] in hashmap and hashmap[s[right]] >= left:
                # the logic here is a little complex, because we are not deleting it
                # we need to ensure that the repeated character lied in the given window
                # between left and right; we need to ensure that left <= hashmap[s[right]] < right
                left = hashmap[s[right]] + 1
            else:
                hashmap[s[right]] = right
                longestsubstring = max(longestsubstring, right-left+1)
                right += 1

        return longestsubstring