[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