覆面算を解く(Ruby/Pythonレクリエーション) ref: http://qiita.com/higuma/items/c44246ebd8e6e4a14a64

alphametics.rb

require 'set'
require 'mathn'

module Alphametics
  def solve(puzzle)
    puzzle = puzzle.upcase
    words = puzzle.scan /[A-Z]+/
    chars = Set.new words.join.each_char
    abort 'Too many letters' if chars.size > 10
    first_chars = Set.new words.select {|w| w.size > 1 }.map {|w| w[0] }
    n = first_chars.size
    sorted_chars = first_chars.to_a.join + (chars - first_chars).to_a.join
    %w[0 1 2 3 4 5 6 7 8 9].permutation(chars.size).each do |guess|
      next if guess[0, n].member? '0'
      expr = puzzle.tr sorted_chars, guess.join
      return expr if eval expr
    end
    return
  end
end

if __FILE__ == $PROGRAM_NAME
  include Alphametics
  ARGV.each do |arg|
    puts arg
    solution = solve arg
    puts solution if solution
  end
end

file0.txt

$ ruby alphametics.rb 'SEND + MORE == MONEY'
SEND + MORE == MONEY
9567 + 1085 == 10652
$ ruby alphametics.rb 'DO + YOU + FEEL == LUCKY'
DO + YOU + FEEL == LUCKY
57 + 870 + 9441 == 10368

file1.txt

$ ruby alphametics.rb 'NORTH / SOUTH == EAST / WEST'
NORTH / SOUTH == EAST / WEST
51304 / 61904 == 7260 / 8760
$ ruby alphametics.rb 'PI * R ** 2 == AREA'
PI * R ** 2 == AREA
96 * 7 ** 2 == 4704

file2.txt

$ ruby alphametics.rb 'MALCOLM + X == MALCOLM'
MALCOLM + X == MALCOLM
1234531 + 0 == 1234531

file4.txt

$ time python3 alphametics.py 'EARTH + AIR + FIRE + WATER == NATURE'
EARTH + AIR + FIRE + WATER == NATURE
67432 + 704 + 8046 + 97364 == 173546

real    0m35.305s
user    0m35.194s
sys     0m0.024s
$ rbenv local 1.9.3-p448        # rubyバージョン変更
$ time ruby alphametics.rb 'EARTH + AIR + FIRE + WATER == NATURE'
EARTH + AIR + FIRE + WATER == NATURE
67432 + 704 + 8046 + 97364 == 173546

real    0m20.051s
user    0m19.921s
sys     0m0.040s
$ rbenv local 2.0.0-p247        # rubyバージョン変更
$ time ruby alphametics.rb 'EARTH + AIR + FIRE + WATER == NATURE'
EARTH + AIR + FIRE + WATER == NATURE
67432 + 704 + 8046 + 97364 == 173546

real    0m24.925s
user    0m24.834s
sys     0m0.032s