1時間以内に解けなければプログラマ失格となってしまう5つの問題(3)

gistfile1.rb

#                                                                                                                                                                                                    
# https://blog.svpino.com/2015/05/08/solution-to-problem-5-and-some-other-thoughts-about-this-type-of-questions                                                                                      
#                                                                                                                                                                                                    
def power(len, sels, arr=[], &block)
  if len == 0 then
    yield arr
  else
    sels.to_a.each { |sel|
      power len-1, sels, arr + [sel], &block
    }
  end
end

power(8,['+','-','']){ |arg|
  # arg = ['', '+', '+', '-', '', '+', '-', ''] => exp = '12+3+4-56+7-89'                                                                                                                            
  exp = ""
  (1..9).each_with_index{ |v,i|
    exp += v.to_s
    exp += arg[i].to_s
  }
  val = eval(exp)
  puts "#{exp} ==> #{val}" if val == 100
}