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

gistfile1.rb

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

power(8,[]){ |arg|
  s = '1'
  (2..9).each { |i|
    s += arg[i-2]
    s += i.to_s
  }
  val = eval(s)
  puts "#{s} ==> #{val}" if val == 100
}