覆面算を ruby で解く。

fukumen.rb

# encoding: utf-8

# See http://web-salad.hateblo.jp/entry/2014/04/06/164312
#  このコードを元に、少し変更して、全解を得るようにした。
#  文字に日本語もあつかえるようにした。
#
#  覆面算の例： http://ja.wikipedia.org/wiki/%E8%A6%86%E9%9D%A2%E7%AE%97
#
DOCUMENT = <<EOS
Find solutions to alphametic equations.

> Alphametics.solve('SEND + MORE == MONEY')
9567 + 1085 == 10652

> Alphametics.solve('AB + 12 = 99')
87 + 12 == 99

> Alphametics.solve('twelve + twenty == answer')
407927 + 407146 == 815073

> Alphametics.solve('ABCDEF * C == CDEFAB')
142857 * 2 == 285714

> Alphametics.solve('kore * are == iroiro')
5943 * 143 == 849849

> Alphametics.solve('a + b + c = ab && b + b + b = c')
1 + 3 + 9 == 13 && 3 + 3 + 3 == 9

> Alphametics.solve('みず * みず = 飲みみず')
76 * 76 == 5776
EOS

module Alphametics
  def solve(puzzle)
    ans = []
    words = puzzle.upcase.split(/[ \=\+\-\*\\^<\>\&\|0-9]+/)
    unique_characters = words.join.split('').uniq
    fail 'Too many letters' if unique_characters.size >= 11 || unique_characters.size == 0
    first_letters = words.map{ |word| word.slice(0) }.uniq
    n = first_letters.size
    characters = (first_letters + (unique_characters - first_letters)).join

    solution = (0..9).to_a.permutation(characters.length) do |guess|
      next if guess.slice(0, n).include?(0)
      equation = puzzle.tr(characters, guess.join)
      ans << equation if eval(equation)
    end
    solution if solution.instance_of?(String)
    ans
  end
  module_function :solve
end

if $PROGRAM_NAME == __FILE__
  puts DOCUMENT and return if ARGV.size.zero?

  ARGV.each do |puzzle|
    puts puzzle
    puzzle = puzzle.gsub('=', '==') unless puzzle.index('==')
    solution = Alphametics.solve(puzzle.upcase)
    puts solution.join("\n") unless solution.nil?
  end
end