Find the Sum of Subsequence Powers
You are given an integer array nums of length n, and a positive integer k.
The power of a subsequence is defined as the minimum absolute difference between any two elements in the subsequence.
Return the sum of powers of all subsequences of nums which have length equal to k.
Since the answer may be large, return it modulo 10^9 + 7.
Example 1
Input
nums = [1,2,3,4], k = 3Output
4There are 4 subsequences in
nums which have length 3: [1,2,3], [1,3,4], [1,2,4], and [2,3,4], and their powers sum to 4.Example 2
Input
nums = [2,2], k = 2Output
0The only subsequence in
nums which has length 2 is [2,2], whose power is |2 - 2| = 0.Constraints
- 2 <= n == nums.length <= 50
- -10^8 <= nums[i] <= 10^8
- 2 <= k <= n