The variance of a string is defined as the largest difference between the number of occurrences of any 2
characters present in the string. Note the two characters may or may not be the same.
Given a string s consisting of lowercase English letters only, return the largest variance possible among all substrings of s
.
A substring is a contiguous sequence of characters within a string.
Example 1:
Input: s = "aababbb"
Output: 3
Explanation:
All possible variances along with their respective substrings are listed below:
 Variance 0 for substrings "a", "aa", "ab", "abab", "aababb", "ba", "b", "bb", and "bbb".
 Variance 1 for substrings "aab", "aba", "abb", "aabab", "ababb", "aababbb", and "bab".
 Variance 2 for substrings "aaba", "ababbb", "abbb", and "babb".
 Variance 3 for substring "babbb".
Since the largest possible variance is 3, we return it.
Example 2:
Input: s = "abcde"
Output: 0
Explanation:
No letter occurs more than once in s, so the variance of every substring is 0.
Constraints:
1 <= s.length <= 10^{4}
s
consists of lowercase English letters.

