m1371.py

"""Find the Longest Substring Containing Vowels in Even Counts
Given the string s, return the size of the longest substring containing each
vowel an even number of times. That is, 'a', 'e', 'i', 'o', and 'u' must appear
an even number of times.

Example 1:

* Input: s = "eleetminicoworoep"
* Output: 13
* Explanation: The longest substring is "leetminicowor" which contains two each
  of the vowels: e, i and o and zero of the vowels: a and u.

Example 2:

* Input: s = "leetcodeisgreat"
* Output: 5
* Explanation: The longest substring is "leetc" which contains two e's.

Example 3:

* Input: s = "bcbcbc"
* Output: 6
* Explanation: In this case, the given string "bcbcbc" is the longest because
  all vowels: a, e, i, o and u appear zero times.

Constraints:

* 1 <= s.length <= 5 x 10^5
* s contains only lowercase English letters.
"""