159.longest-substring-with-at-most-two-distinct-characters.py

#
# @lc app=leetcode id=159 lang=python3
#
# [159] Longest Substring with At Most Two Distinct Characters
#

# @lc code=start
class Solution:
    def lengthOfLongestSubstringTwoDistinct(self, s: str) -> int:
        char_count = {}
        left = 0
        res = 0

        for right in range(len(s)):
            char_count[s[right]] = char_count.get(s[right], 0) + 1

            while len(char_count) > 2:
                char_count[s[left]] -= 1
                if char_count[s[left]] == 0:
                    del char_count[s[left]]
                left += 1

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

        return res
# @lc code=end