Solve the programming task below in a Python markdown code block.
For a finite set of integers X, let f(X)=\max X - \min X.
Given are N integers A_1,...,A_N.
We will choose K of them and let S be the set of the integers chosen. If we distinguish elements with different indices even when their values are the same, there are {}_N C_K ways to make this choice. Find the sum of f(S) over all those ways.
Since the answer can be enormous, print it \bmod (10^9+7).

-----Constraints-----
 - 1 \leq N \leq 10^5
 - 1 \leq K \leq N
 - |A_i| \leq 10^9

-----Input-----
Input is given from Standard Input in the following format:
N K
A_1 ... A_N

-----Output-----
Print the answer \bmod (10^9+7).

-----Sample Input-----
4 2
1 1 3 4

-----Sample Output-----
11

There are six ways to choose S: \{1,1\},\{1,3\},\{1,4\},\{1,3\},\{1,4\}, \{3,4\} (we distinguish the two 1s). The value of f(S) for these choices are 0,2,3,2,3,1, respectively, for the total of 11.