Given a digit string s, return the number of unique substrings of s where every digit appears the same number of times.

 

Example 1:

Input: s = "1212"
Output: 5
Explanation: The substrings that meet the requirements are "1", "2", "12", "21", "1212".
Note that although the substring "12" appears twice, it is only counted once.

Example 2:

Input: s = "12321"
Output: 9
Explanation: The substrings that meet the requirements are "1", "2", "3", "12", "23", "32", "21", "123", "321".

 

Constraints:

• 1 <= s.length <= 1000
• s consists of digits.