fukumen.rb

fukumen.rb

# 問題: https://twitter.com/nada_mathclub/status/1256418924737880069
#     : vivid * vive = brillante の覆面算を解く
# 解答: 62621 * 6267 = 392445807

def solve(v, i, d, e)
  return nil if v == 0
  vivid = [v, i, v, i, d].inject(0) {|sum, x| sum * 10 + x}
  vive = [v, i, v, e].inject(0) {|sum, x| sum * 10 + x}
  brillante = Enumerator.new do |e|
    t = (vivid * vive)
    loop do
      e << [t % 10, t, (t = t/10)]
    end
  end.take_while {|t| t[1] != 0}.map(&:first)
  return nil if brillante.size < 9
  used    = {v => true, i => true, d => true, e => true}
  mapping = {'v' => v, 'i' => i, 'd' => d, 'e' => e}
  result = 'brillante'.chars.reverse.map.with_index do |c, index|
    digit = brillante[index]
    if mapping.has_key?(c)
      mapping[c] === digit
    else
      next false if used.has_key?(digit) || (index === 8 && digit == 0)
      mapping[c] = digit
      used[digit] = true
    end
  end
  result.all? ? [vivid, vive, vivid * vive] : nil
end

(0..9).to_a.permutation(4) do |nums|
  if (res = solve(*nums))
    vivid, vive, brillante = res
    puts "#{vivid} * #{vive} = #{vivid * vive}"
  end
end