README.md

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: 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.

Solutions (Rust)

1. Solution

impl Solution {
    pub fn count_homogenous(s: String) -> i32 {
        let s = s.as_bytes();
        let mut count = 1;
        let mut ret = 1;

        for i in 1..s.len() {
            if s[i] != s[i - 1] {
                count = 0;
            }

            count += 1;
            ret = (ret + count) % 1_000_000_007;
        }

        ret
    }
}