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(2)

gistfile1.rb

#                                                                                                                                                                                                    
# https://blog.svpino.com/2015/05/08/solution-to-problem-5-and-some-other-thoughts-about-this-type-of-questions                                                                                      
#                                                                                                                                                                                                    
def power(n, alts, &block)
  _power(n, 0, [], alts, &block)
end

def _power(total, level, res, alts, &block)
  if level < total then
    alts.each { |op|
      res[level] = op
      _power total, level+1, res, alts, &block
    }
  else
    yield res
  end
end

power(8,['+','-','']){ |arg|
  # arg = ['', '+', '+', '-', '', '+', '-', ''] => exp = '12+3+4-56+7-89'                                                                                                                            
  exp = []
  (1..9).each_with_index{ |v,i| exp[i*2] = v }
  arg.each_with_index{ |v,i| exp[i*2+1] = v }
  exp = exp.join('')
  val = eval(exp)
  puts "#{exp} ==> #{val}" if val == 100