Given a string s consisting only of characters a, b and c. Return the number of substrings containing at least one occurrence of all these characters a, b and c. Example 1: Input: s = "abcabc" Output: 10 Explanation: The substrings containing at least one occurrence of the characters a, b and c are "abc", "abca", "abcab", "abcabc", "bca", "bcab", "bcabc", "cab", "cabc" and "abc" (again). Example 2: Input: s = "aaacb" Output: 3 Explanation: The substrings containing at least one occurrence of the characters a, b and c are "aaacb", "aacb" and "acb". Example 3: Input: s = "abc" Output: 1 Constraints: 3 <= s.length <= 5 x 10^4 s only consists of a, b or c characters.