3299. Sum of Consecutive Subsequences

We call an array arr of length n consecutive if one of the following holds:

• arr[i] - arr[i - 1] == 1 for all 1 <= i < n.
• arr[i] - arr[i - 1] == -1 for all 1 <= i < n.

The value of an array is the sum of its elements.

For example, [3, 4, 5] is a consecutive array of value 12 and [9, 8] is another of value 17. While [3, 4, 3] and [8, 6] are not consecutive.

Given an array of integers nums, return the sum of the values of all consecutive non-empty subsequences.

Since the answer may be very large, return it modulo 109 + 7.

Note that an array of length 1 is also considered consecutive.

Example 1:

Example 2:

Constraints:

• 1 <= nums.length <= 105
• 1 <= nums[i] <= 105