input

2 7

rabbit.rb

class Rabbit

  @@result = 0

  def initialize(path = "./input")
    File.open(path, "r") do |file|  
      file.each_line do |line|
        line = line.split
        combinations(line[0].to_i, line[1].to_i)
        p @@result
        
      end
    end
  end  

private 
  def combinations(k, n, i = 0)
    i += 1
    @@result += combinations(k, n - i, i) if i < k 
  end 
end

Rabbit.new