LeetCode 3 - Longest Substring Without Repeating Characters - 2023.10.13 solution

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        """ Thought: We can have two pointers, with a set listing
        all the characters contained in the span between them. We
        advance the right pointer until we hit a duplicate, at
        which point we advance the left pointer. We use a separate
        variable to keep track of the largest substring we've
        encountered.
        """
        l = 0
        r = 0

        if len(s) == 0:
            return 0

        span_set = set([s[0]])
        largest_substring = 1

        while r < len(s) - 1:
            r += 1
            while s[r] in span_set:
                span_set.remove(s[l])
                l += 1
            span_set.add(s[r])
            largest_substring = max(largest_substring, r - l + 1)

        return largest_substring