advent_day_3.rb

# http://adventofcode.com/day/3 - part 1
#
# instructions - String with sequentials commands for which direction to take.
# ^ north, v south, > east, < west
#
# Returns an integer of the area of wrapping paper required, in square feet.
def houses_visited(instructions)
  visited = [[0, 0]]

  x = 0
  y = 0

  instructions.split("").each do |move|
    if move == "^" # north
      y += 1
    elsif move == "v" # south
      y -= 1
    elsif move == ">" # east
      x += 1
    elsif move == "<" # west
      x -= 1
    end

    position = [x, y]

    visited << position unless visited.include?(position)
  end

  visited.size
end


# http://adventofcode.com/day/3 - part 2
#
# instructions - String with sequentials commands for which direction to take.
# ^ north, v south, > east, < west
#
# Returns an integer of the area of wrapping paper required, in square feet.
def houses_visited_by_santa_and_robot(instructions)
  visited = [[0, 0]]

  santa = { x: 0, y: 0 }
  robot = { x: 0, y: 0 }

  instructions.split("").each_with_index do |move, i|
    person = i.even? ? santa : robot

    if move == "^" # north
      person[:y] += 1
    elsif move == "v" # south
      person[:y] -= 1
    elsif move == ">" # east
      person[:x] += 1
    elsif move == "<" # west
      person[:x] -= 1
    end

    position = [person[:x], person[:y]]

    visited << position unless visited.include?(position)
  end

  visited.size
end