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Given a string S, the task is to count number of subsequences of the form aibjck, where i >= 1, j >=1 and k >= 1.
Note:
1. Two subsequences are considered different if the set of array indexes picked for the 2 subsequences are different.
2. For large test cases, the output value will be too large, return the answer MODULO 10^9+7
Example 1:
Input:
S = "abbc"
Output: 3
Explanation: Subsequences are abc, abc and abbc.
Example 2:
Input:
S = "abcabc"
Output: 7
Explanation: Subsequences are abc, abc,
abbc, aabc abcc, abc and abc.
Your Task:
You don't need to read input or print anything. Your task is to complete the function fun() which takes the string S as input parameter and returns the number of subsequences which follows given condition.
Expected Time Complexity: O(Length of String).
Expected Auxiliary Space: O(1) .
Constraints:
1 <= |S| <= 105
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