Longest Substring with At Most Two Distinct

lcpy gen -n 159   # by problem number
lcpy gen -s longest_substring_with_at_most_two_distinct_characters   # by problem name

Input: s = "eceba"
Output: 3
Explanation: The substring is "ece" which its length is 3.

Input: s = "ccaabbb"
Output: 5
Explanation: The substring is "aabbb" which its length is 5.

class Solution:
    # Time: O(n)
    # Space: O(1)
    def length_of_longest_substring_two_distinct(self, s: str) -> int:
        count: dict[str, int] = {}
        left = 0
        longest = 0
        for right, ch in enumerate(s):
            count[ch] = count.get(ch, 0) + 1
            while len(count) > 2:
                left_ch = s[left]
                count[left_ch] -= 1
                if count[left_ch] == 0:
                    del count[left_ch]
                left += 1
            longest = max(longest, right - left + 1)
        return longest