Count Substrings That Include a,b and c

### Problem The string s uses only a,b,c. Return the number of contiguous substring occurrences containing at least one of each of these three letters. Equal substring text at different positions counts separately. ```cpp class Solution { public: int numberOfSubstrings(string s); }; ``` ### Examples **Example 1:** ```text Input: s = "abca" Output: 3 Explanation: The qualifying intervals contain abc,abca,and bca. ``` **Example 2:** ```text Input: s = "aaaa" Output: 0 Explanation: No substring contains b or c. ``` ### Constraints - s has length 3 to 50000. - Its characters are only a,b or c. ### Contract considerations All three letters are required; having at least three characters is insufficient by itself. ```hint Read the boundary condition Count substring occurrences by position. Include strings missing a required letter and strings with repeated copies of all three letters. ``` ### Boundary reminders All three letters are required; having at least three characters is insufficient by itself.