Problem:
Score : 500 points

Problem Statement

Given are N integers A_1,\ldots,A_N.

We will choose exactly K of these elements. Find the maximum possible product of the chosen elements.

Then, print the maximum product modulo (10^9+7), using an integer between 0 and 10^9+6 (inclusive).

Constraints

1 \leq K \leq N \leq 2\times 10^5

|A_i| \leq 10^9

Input

Input is given from Standard Input in the following format:

N K
A_1 \ldots A_N

Output

Print the maximum product modulo (10^9+7), using an integer between 0 and 10^9+6 (inclusive).

Sample Input 1

4 2
1 2 -3 -4

Sample Output 1

12

The possible products of the two chosen elements are 2, -3, -4, -6, -8, and 12, so the maximum product is 12.

Sample Input 2

4 3
-1 -2 -3 -4

Sample Output 2

1000000001

The possible products of the three chosen elements are -24, -12, -8, and -6, so the maximum product is -6.

We print this value modulo (10^9+7), that is, 1000000001.

Sample Input 3

2 1
-1 1000000000

Sample Output 3

1000000000

The possible products of the one chosen element are -1 and 1000000000, so the maximum product is 1000000000.

Sample Input 4

10 10
1000000000 100000000 10000000 1000000 100000 10000 1000 100 10 1

Sample Output 4

999983200

Be sure to print the product modulo (10^9+7).

Solution in Ruby (2.7.1) (judge verdict: Wrong Answer)

N, K = gets.split.map(&:to_i)
AS = gets.split.map(&:to_i)

def nums
  return AS if N == K

  sorted = AS.sort_by(&:abs).reverse

  return sorted.last(K) if AS.all? { |n| n < 0 } && K % 2 == 1

  nums = sorted.first(K)

  return nums unless nums.select { |n| n < 0 }.count % 2 == 1

  posplus = begin
      plus = sorted[K..-1].find { |n| n > 0 } || 0
      swap = nums.reverse.find { |n| n < 0 } || 0
      [plus, swap]
    end

  negplus = begin
      plus = sorted[K..-1].find { |n| n < 0 } || 0
      swap = nums.reverse.find { |n| n > 0 } || 0
      [plus, swap]
    end

  swaps = if (posplus[0] * posplus[1]).abs >= (negplus[0] * negplus[1]).abs
      posplus
    else
      negplus
    end
  nums.length.times.each do |i|
    if nums[i] == swaps[1]
      nums[i] = swaps[0]
      break
    end
  end
  nums
end

result = 1
mod = 10 ** 9 + 7
nums.each do |n|
  result = result * n % mod
end

puts result