The beauty of a string is the difference in frequencies between the most frequent and least frequent characters.

- For example, the beauty of `"abaacc"` is `3 - 1 = 2`.

Given a string `s`, return the sum of beauty of all of its substrings.

Example 1:

    Input: s = "aabcb"
    Output: 5
    Explanation: The substrings with non-zero beauty are ["aab","aabc","aabcb","abcb","bcb"], each with beauty equal to 1.

Example 2:

    Input: s = "aabcbaa"
    Output: 17

Constraints:

- `1 <= s.length <= 500`
- `s` consists of only lowercase English letters.