Sum of Subarrays
Medium Accuracy: 19.98% Submissions: 346 Points: 4

Given an array A[] with N elements , you need to find the sum all sub arrays of array A. Since the sum could be very large print the sum modulo (109+7).


Example 1:

Input:
N = 3
A[] = {1, 2, 3}
Output: 20
Explanation:
All subarrays are [1], [2], [3],
[1,2], [2,3], [1,2,3].
Thus total sum is 20.

 

Example 2:

Input:
N = 2
A[] = {1, 3}
Output: 8


Your Task:  
You don't need to read input or print anything. Your task is to complete the function subarraySum() which takes the array A[] and its size N as inputs and returns the sum.


Expected Time Complexity: O(N)
Expected Auxiliary Space: O(1)


Constraints :
1 <= N <= 105
1 <= A[] <= 109

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