class DirectionString
  attr_reader :string, :start_position

  def initialize(string, start_position=[1, 1])
    @string = string
    @start_position = start_position
  end

  def final_position
    return start_position if string.empty?

    self.class.new(string[1..], next_position).final_position
  end

  def next_position
    case string[0]
    when "D"
      [start_position[0], start_position[1] + 1]
    when "U"
      [start_position[0], start_position[1] - 1]
    when "L"
      [start_position[0] - 1, start_position[1]]
    when "R"
      [start_position[0] + 1, start_position[1]]
    end.map{ |pos| pos.clamp(0, 2) }
  end
end

def reduce(array, initial_value)
  acc = initial_value
  array.each do |value|
    acc = yield(acc, value)
  end
  acc
end

input = STDIN.read.chomp
direction_strings = input.split

KEYPAD = [[ 1, 2, 3 ],
          [ 4, 5, 6 ],
          [ 7, 8, 9 ]]

def keypad_digit(position)
  x, y = position
  KEYPAD[y][x]
end

digits = [] 
direction_strings.inject([1, 1]) do |acc, x|
  y = DirectionString.new(x, acc).final_position
  digits << keypad_digit(y)
  y
end

puts "Part 1: #{digits.join}"