Given a string s, return the length of the longest substring that contains at most two distinct characters.
Example 1:
Input: s = "eceba" Output: 3 Explanation: The substring is "ece" which its length is 3.
Example 2:
Input: s = "ccaabbb" Output: 5 Explanation: The substring is "aabbb" which its length is 5.
Constraints:
1 <= s.length <= 104sconsists of English letters.