頭の体操

#!/usr/bin/env ruby
# coding: utf-8

def t(p,m,o,b)
  2*p*m - o*b == 7
end

result = []

(1111..9999).each do |i|
  p,m,o,b = i.to_s.split(//).map do |s|
    s.to_i
  end
  if t(p,m,o,b)
    result << (p>m ? [m,p] : [p,m]) + (o>b ? [b,o] : [o,b])
  end
end

p result.uniq