1759. Count Number of Homogenous Substrings

https://leetcode.com/problems/count-number-of-homogenous-substrings

Description

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.

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