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Count subsequences of type a^i, b^j, c^k
Medium Accuracy: 28.27% Submissions: 3706 Points: 4

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, 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| <= 103

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Count subsequences of type a^i, b^j, c^k

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