覆面算（汎用版）

main.rb

# 問題:
#   http://hidesugar.web.fc2.com/ym2/ym2musikuizan2.txt
#   ABCDEF * G = FABCDE
# 解答: 230769 * 4 = 923076

def solve(sx, sy, sz, mapping)
  x = sx.inject(0) {|sum, x| sum * 10 + mapping[x]}
  y = sy.inject(0) {|sum, y| sum * 10 + mapping[y]}
  z = Enumerator.new do |e|
    t = (x * y)
    loop do
      e << [t % 10, t, (t = t/10)]
    end
  end.take_while {|t| t[1] != 0}.map(&:first)
  used = mapping.values.map {|k| [k, true]}.to_h
  result = sz.reverse.map.with_index do |c, index|
    digit = z[index]
    if mapping.has_key?(c)
      mapping[c] === digit && used[digit]
    else
      next false if used.has_key?(digit)
      mapping[c] = digit
      used[digit] = true
    end
  end
  result.all? ? [x, y, z, mapping] : nil
end

def explore(sx, sy, sz)
  sx = sx.chars
  sy = sy.chars
  sz = sz.chars
  vals = (sx + sy).uniq

  (0..9).to_a.permutation(vals.size) do |nums|
    fail if vals.size != nums.size
    if (res = solve(sx, sy, sz, vals.zip(nums).to_h))
      x, y, z, mapping = res
      puts "#{x} * #{y} = #{x * y}"
    end
  end  
end

# explore('vivid', 'vive', 'brillante')
explore('ABCDEF', 'G', 'FABCDE')