# 1759. 统计同构子字符串的数目

class Solution {
public:
    int countHomogenous(string s) {
        long long MOD = 1e9 + 7;
        int left = 0;
        long long ans = 0;
        for (int i = 1; i < s.length(); i++) {
            if (s[i] != s[left]) {
                ans += (i - left) * (i - left + 1) / 2;
                ans %= MOD;
                left = i;
            }
        }
        ans += (s.length() - left) * (s.length() + 1 - left) / 2;
        return ans % MOD;
    }
};