Given string s consisting only a,b,c. return the number of substrings containing at least one occurrence of all these characters a, b, and c.
Example 1:
Input:
abcabc
Output:
10
Explanation:
The required substrings are "abc", "abca", "abcab", "abcabc",
"bca", "bcab", "bcabc", "cab", "cabc" and "abc".
Example 2:
Input:
aaacb
Output:
3
Your Task:
You don't have to read input or print anything. Your task is to complete the function countSubstring() which takes the string s and returns the count of substring having at least a,b,c.
Expected Time Complexity: O(n)
Expected Space Complexity: O(1)
Constraint:
3<=s.length<=5 x 10^{4 }
S only contains a,b,c.

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