project euler 032

032.rb

require 'set'

s = Set.new

class Array
  def pandigital?(r=(1..9))
    len = r.last - r.first + 1
    if length != len
      false
    else
      ary = clone
      while ary.last==0
        ary.pop
      end
      ary.select{|x| r===x}.uniq.length == len
    end
  end
end

class Integer
  def digits(base=10)
    x = self
    a = []
    while x!=0
      x,r = x.divmod(base)
      a << r;
    end
    return a
  end
end

1.upto(99) do |a|
  a.upto(9999) do |b|
    c = a * b
    digits = (c.digits + a.digits + b.digits)
    break if digits.length > 9
    if digits.pandigital? 1..9
      s << c
    end
  end
end

puts s.reduce(:+)