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Count Number of Homogenous Substrings

Given a string s, return the number of homogenous substrings of s.

Given a string s, return the number of homogenous substrings of s. Since the answer may be too large, return it modulo 10^9 + 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.

Count Number of Homogenous Substrings diagram

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 <= 10^5
  • s consists of lowercase letters.

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