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

A string is homogenous if all the characters of the string are the same.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = "abbcccaa"

Output: 13

Explanation: The homogenous substrings are listed as below:

"a"   appears 3 times.

"aa"  appears 1 time.

"b"   appears 2 times.

"bb"  appears 1 time.

"c"   appears 3 times.

"cc"  appears 2 times.

"ccc" appears 1 time.

3 + 1 + 2 + 1 + 3 + 2 + 1 = 13.

Example 2:

Input: s = "xy"

Output: 2

Explanation: The homogenous substrings are "x" and "y".

Example 3:

Input: s = "zzzzz"

Output: 15

Constraints:

• 1 <= s.length <= 105
• s consists of lowercase letters.