MCC #0 solution

mcc-0-maurizio.rb

class Combinations
  def initialize options = {}
    @input = options[:input]
    @lengths = @input.map &:size
    @counters = @lengths.map { 0 }
    @current = @input.map {|line| line[0]}.join
  end

  def each
    begin
      yield @current
    end while clock!
  end

  private

  def clock!
    index = 0
    while index < @input.size && (@counters[index] += 1) == @lengths[index]
      @counters[index] %= @lengths[index]
      update_current! index
      index += 1
    end
    if index < @input.size
      update_current! index
      true
    else
      false
    end
  end

  def update_current! index
    @current[index] = @input[index][@counters[index]]
  end
end

class Solution
  def initialize
    input = STDIN.readlines.map &:strip
    combinations = Combinations.new input: input
    combinations.each do |combination|
      puts combination
    end
  end
end

Solution.new