Given a string `s`, return the maximum number of ocurrences of any substring under the following rules:

- The number of unique characters in the substring must be less than or equal to `maxLetters`.
- The substring size must be between `minSize` and `maxSize` inclusive.

Example 1:

    Input: s = "aababcaab", maxLetters = 2, minSize = 3, maxSize = 4
    Output: 2
    Explanation: Substring "aab" has 2 ocurrences in the original string.
    It satisfies the conditions, 2 unique letters and size 3 (between minSize and maxSize).

Example 2:

    Input: s = "aaaa", maxLetters = 1, minSize = 3, maxSize = 3
    Output: 2
    Explanation: Substring "aaa" occur 2 times in the string. It can overlap.

Constraints:

- `1 <= s.length <= 105`
- `1 <= maxLetters <= 26`
- `1 <= minSize <= maxSize <= min(26, s.length)`
- `s` consists of only lowercase English letters.