numbers.rb

numbers = [1,2,3,4,5,6,7,8,9]
target = 50
k = 5

def calculate_sum(inputs, k)
  inputs.each_index do |i|
    pairing = [inputs[i]]

    inputs.each_index do |j|
      next if i == j
      if pairing.size == k
        yield pairing
        pairing = [inputs[i]]
      end

      pairing << inputs[j]
    end
  end
end

calculate_sum(numbers, k) do |set|
  if set.inject(&:+) == target
    puts set.inspect
    exit
  end
end

puts "No combination exists"
exit 1