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.
Examples
Example 1
Input: s = "abbcccaa"
Output: 13
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
The homogenous substrings are "x" and "y".
Example 3
Input: s = "zzzzz"
Output: 15
Constraints
1 <= s.length <= 10⁵sconsists of lowercase letters.