A subsequence of a string is good if it is not empty and the frequency of each one of its characters is the same.

Given a string s, return the number of good subsequences of s. Since the answer may be too large, return it modulo 109 + 7.

A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.

 

Example 1:

Input: s = "aabb"
Output: 11
Explanation: The total number of subsequences is 24. There are five subsequences which are not good: "aabb", "aabb", "aabb", "aabb", and the empty subsequence. Hence, the number of good subsequences is 24-5 = 11.

Example 2:

Input: s = "leet"
Output: 12
Explanation: There are four subsequences which are not good: "leet", "leet", "leet", and the empty subsequence. Hence, the number of good subsequences is 24-4 = 12.

Example 3:

Input: s = "abcd"
Output: 15
Explanation: All of the non-empty subsequences are good subsequences. Hence, the number of good subsequences is 24-1 = 15.

 

Constraints:

• 1 <= s.length <= 104
• s consists of only lowercase English letters.