[LC] 159. Longest Substring with At Most Two Distinct Characters

Given a string s , find the length of the longest substring t  that contains at most 2 distinct characters.

Example 1:

Input: "eceba"
Output: 3
Explanation: tis "ece" which its length is 3.

Example 2:

Input: "ccaabbb"
Output: 5
Explanation: tis "aabbb" which its length is 5.

Time: O(N)
Space: O(N)

class Solution:
    def lengthOfLongestSubstringTwoDistinct(self, s: str) -> int:
        res = 0
        start, end, count = 0, 0, 0
        my_dict = {}
        while end < len(s):
            end_char = s[end]
            end_freq = my_dict.get(end_char, 0)
            my_dict[end_char] = end_freq + 1
            if end_freq == 0:
                count += 1
            end += 1
            // cannot use count <= 2 to get res b/c end will run before start
            while count > 2:
                start_char = s[start]
                start_freq = my_dict[start_char]
                my_dict[start_char] = start_freq - 1
                if start_freq == 1:
                    count -= 1
                start += 1
            res = max(res, end - start)
        return res