Value of subsequences - MarisaOJ: Marisa Online Judge

The value of an array

$B$ is the maximum element in

$B$ . Given an array

$A$ of

$n$ integers. Find the sum of value of all subsequences of length

$k$ of

$A$ . ### Input - The first line contains 2 integers

$n, k$ . - The second line contains

$n$ integers

$A_i$ . ### Output - Print the sum, modulo

$10^9+7$ . ### Constraints -

$1 \le k \le n \le 10^5$ . ### Example Input:

$4 2 6 7 6 5$

Output:

$39$

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Math

Combinatorics

Rating

1400

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Solution