Count Substrings with Only One Distinct Letter

给一个String, 问里面多少个substring只有一个不同的字符.

首先一个string, 比如aaaaa, 那么里面的只有一个不同字符的是n*(n+1) / 2个子string. 然后找就行了.

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