Given a string S, return the number of substrings that have only one distinct letter.
Example 1:
Input: S = "aaaba" Output: 8 Explanation: The substrings with one distinct letter are "aaa", "aa", "a", "b". "aaa" occurs 1 time. "aa" occurs 2 times. "a" occurs 4 times. "b" occurs 1 time. So the answer is 1 + 2 + 4 + 1 = 8.
Example 2:
Input: S = "aaaaaaaaaa" Output: 55
Constraints:
1 <= S.length <= 1000S[i] consists of only lowercase English letters.struct Solution;
impl Solution {
fn count_letters(s: String) -> i32 {
let mut prev: Option<char> = None;
let mut count = 0;
let mut sum = 0;
for c in s.chars() {
if let Some(prev_c) = prev {
if c == prev_c {
count += 1;
} else {
sum += count * (count + 1) / 2;
count = 1;
prev = Some(c);
}
} else {
count = 1;
prev = Some(c);
}
}
sum += count * (count + 1) / 2;
sum as i32
}
}
#[test]
fn test() {
let s = "aaaba".to_string();
assert_eq!(Solution::count_letters(s), 8);
let s = "aaaaaaaaaa".to_string();
assert_eq!(Solution::count_letters(s), 55);
}