891. Sum of Subsequence Widths
Hard
656
164

The width of a sequence is the difference between the maximum and minimum elements in the sequence.

Given an array of integers `nums`, return the sum of the widths of all the non-empty subsequences of `nums`. Since the answer may be very large, return it modulo `109 + 7`.

A subsequence is a sequence that can be derived from an array by deleting some or no elements without changing the order of the remaining elements. For example, `[3,6,2,7]` is a subsequence of the array `[0,3,1,6,2,2,7]`.

Example 1:

```Input: nums = [2,1,3]
Output: 6
Explanation: The subsequences are [1], [2], [3], [2,1], [2,3], [1,3], [2,1,3].
The corresponding widths are 0, 0, 0, 1, 1, 2, 2.
The sum of these widths is 6.
```

Example 2:

```Input: nums = [2]
Output: 0
```

Constraints:

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