階乗フィーバー数問題

codeiq39.rb

#!/usr/bin/env ruby
# http://riverplus.net/39/
# https://twitter.com/riverplus/status/754322322220158977
#


class Factorial
  @@f = 1
  @@now = 0

  def self.next
    @@now += 1
    @@f *= @@now
  end

  def self.index
    @@now + 1
  end
end

1.upto(12) do |i|
  puts "#{Factorial.index}: #{Factorial.next}"
end

def solve?(f)
  ns = f.to_s[0...6].split ''
  return false if ns.size < 6
  (ns - [ns.first]).empty?
end

i = 0
loop do
  i += 1
  f = Factorial.next
  if solve? f
    puts i
  end
end

$ time ruby main.rb
main.rb:8:in `factorial': stack level too deep (SystemStackError)
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
    from main.rb:11:in `factorial'
     ... 10068 levels...
    from main.rb:17:in `solve'
    from main.rb:25:in `block in <main>'
    from main.rb:23:in `loop'
    from main.rb:23:in `<main>'
ruby main.rb  134.20s user 21.95s system 99% cpu 2:37.37 total