day3.rb

require 'byebug'
class Wire
  attr_reader :runs

  def initialize(wire_path)
    x, y = 0, 0
    @runs = []
    steps = 0
    wire_path.split(',').each do |wire_run|
      start_x, start_y = x, y
      direction = wire_run.slice!(0)
      length = wire_run.to_i
      case direction
      when 'R'
        x += length
      when 'L'
        x -= length
      when 'U'
        y += length
      when 'D'
        y -= length
      else
        raise "What direction is #{direction}?!"
      end
      @runs << WireRun.new(start_x, start_y, x, y, direction, steps)
      steps += length
    end
  end

  def intersections(wire2)
    @runs.flat_map do |run|
      wire2.runs.collect { |run2| run.intersection(run2) }.compact
    end
  end

  def intersect(wire2)
    intersections(wire2).collect { |x,y| x.abs + y.abs }.min
  end

  def intersecting_wire_runs(wire2)
    @runs.flat_map do |run|
      wire2.runs.select { |run2| run.intersection(run2) }.collect { |run2| [run, run2] }
    end
  end

  def intersect_minimum_signal_delay(wire2)
    intersecting_wire_runs(wire2).collect do |run1, run2|
      point = run1.intersection(run2)
      # byebug
      run1.steps_at(point) + run2.steps_at(point)
    end.min
  end
end

class WireRun
  attr_reader :x1, :y1, :x2, :y2
  def initialize(x1, y1, x2, y2, direction, previous_steps)
    @x1, @y1, @x2, @y2 = x1, y1, x2, y2
    @previous_steps = previous_steps
    @direction = direction
  end

  def to_s
    "#{[x1, y1]} -> #{[x2, y2]}"
  end

  def vertical?
    @x1 == @x2
  end

  def central_port?
    (@x1 == 0 && @y1 == 0) || (@x2 == 0 && @y2 == 0)
  end

  def steps_at(point)
    x, y = point
    raise "does not cross" if vertical? && !(@x1 == x && length_includes?(@y1,@y2,y))
    raise "does not cross" if !vertical? && !(@y1 == y && length_includes?(@x1,@x2,x))
    # do negative values matter?
    steps_so_far =
      case @direction
      when 'U'
        y - @y1
      when 'D'
        @y1 - y
      when 'L'
        @x1 - x
      when 'R'
        x - @x1
      end
    @previous_steps + steps_so_far
  end

  def intersection(run2)
    return nil if vertical? && run2.vertical?
    return nil if central_port? && run2.central_port?

    if vertical?
      return nil unless length_includes?(@y1,@y2,run2.y1)
      return nil unless length_includes?(run2.x1,run2.x2,@x1)
      return [@x1, run2.y1]
    end
    # we're horizontal
    return nil unless length_includes?(@x1,@x2,run2.x1)
    return nil unless length_includes?(run2.y1,run2.y2,@y1)
    [run2.x1, @y1]
  end
private
  def length_includes?(test1, test2, subject)
    if test1 > test2
      return (test2..test1).include? subject
    end
    (test1..test2).include? subject
  end
end

if __FILE__ == $0
  wire1 = Wire.new(DATA.readline)
  wire2 = Wire.new(DATA.readline)
  print "Shortest Manhattan distance for intersections: #{wire1.intersect(wire2)}\n"
  print "Fewest combined steps for intersections: #{wire1.intersect_minimum_signal_delay(wire2)}\n"
end

__END__
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