Find all the substrings by using two loops. Use a variable max to record the maximum length of the substring that meets the condition. For each substring, count the numbers of vowels. If all numbers ...

Description 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.