zero.rb

#!/usr/bin/env ruby
class Anagram
  def initialize filename
    @cols = []
    File.open filename do |file|
      file.each do |line|
        @cols << line.strip
      end
    end
  end

  def all_combinations
    combinations = []
    each_combination do |combination|
      combinations << combination
    end
    combinations
  end

  private

  def each_combination &block
    clear_indexes_cache
    # combinations size
    @cols.map(&:size).inject(&:*).times do
      block.call next_combination
    end
  end

  def clear_indexes_cache
    @indexes = Hash.new 0
  end

  def next_combination
    @can_advance = true
    @cols.size.times.map { |col| next_letter col }.join
  end

  def next_letter column
    index = @indexes[column]
    letter = @cols[column].chars.to_a[index]
    advance_index column if can_advance_index column
    letter
  end

  def can_advance_index column
    @can_advance && @cols[column].size > (@indexes[column] + 1)
  end

  def advance_index column
    @indexes[column] = @indexes[column] + 1
    column.times { |col| @indexes[col] = 0 }
    @can_advance = false
  end
end

if __FILE__==$0
  t = Time.now
  a = Anagram.new 'in.txt'
  puts a.all_combinations.join "\n"
  puts "Time spent: #{Time.now - t}"
end