count_substrings_with_only_one_distinct_letter.cpp

/*
1180. Count Substrings with Only One Distinct Letter
Easy

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
*/

class Solution {
public:
    int countLetters(string S) {
        int count=1,sum=0;
        for(int i=1;i<S.length();i++){
            if(S[i]==S[i-1])
                count++;
            else{
                sum+=(count*(count+1)/2);
                count=1;
            }
        }
        sum+=(count*(count+1)/2);
           return sum; 
    }
};