1180. Count Substrings with Only One Distinct Letter

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 <= 1000
• S[i] consists of only lowercase English letters.