Given an array of integers arr, find the sum of `min(b)`, where `b` ranges over every (contiguous) subarray of `arr`. Since the answer may be large, return the answer modulo `109 + 7`.

Example 1:

    Input: arr = [3,1,2,4]
    Output: 17
    Explanation:
    Subarrays are [3], [1], [2], [4], [3,1], [1,2], [2,4], [3,1,2], [1,2,4], [3,1,2,4].
    Minimums are 3, 1, 2, 4, 1, 1, 2, 1, 1, 1.
    Sum is 17.

Example 2:

    Input: arr = [11,81,94,43,3]
    Output: 444

Constraints:

- `1 <= arr.length <= 3 * 104`
- `1 <= arr[i] <= 3 * 104`