LeetCode 1759. Count Number of Homogenous Substrings
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: 13Explanation: 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: 2Explanation: The homogenous substrings are "x" and "y".
Example 3:
Input: s = "zzzzz"Output: 15
Constraints:
1 <= s.length <= 105sconsists of lowercase letters.
math：
Runtime: 15 ms, faster than 62.58% of Java online submissions for Count Number of Homogenous Substrings.
Memory Usage: 44.7 MB, less than 5.81% of Java online submissions for Count Number of Homogenous Substrings.
