2019: Day 3 Part 1

2019/day3/part1.rb

@@ -0,0 +1,92 @@
+# frozen_string_literal: true
+
+require 'pp'
+
+input = File.read(File.join(__dir__, 'input'))
+
+def wires(input)
+  input.lines.map do |line|
+    wire_points(line.strip.split(','))
+  end
+end
+
+class Point
+  attr_reader :x, :y
+  def initialize(x, y)
+    @x = x
+    @y = y
+  end
+
+  def inspect
+    "Point(#{x}, #{y})"
+  end
+
+  def hash
+    [x, y].hash
+  end
+
+  def eql?(other)
+    x == other.x && y == other.y
+  end
+
+  def right(dy)
+    Point.new(x, y + dy)
+  end
+
+  def left(dy)
+    Point.new(x, y - dy)
+  end
+
+  def down(dx)
+    Point.new(x - dx, y)
+  end
+
+  def up(dx)
+    Point.new(x + dx, y)
+  end
+
+  def move(direction, delta)
+    case direction
+    when 'U'
+      up(delta)
+    when 'D'
+      down(delta)
+    when 'L'
+      left(delta)
+    when 'R'
+      right(delta)
+    else
+      raise StandardError, "Unexpected move direction: #{direction}"
+    end
+  end
+
+  def manhattan_distance_to(other)
+    (x - other.x).abs + (y - other.y).abs
+  end
+end
+
+def wire_points(moves)
+  pos = Point.new(0, 0)
+  # NOTE: We don't include the origin in the list of points because that's not
+  # considered a valid intersection.
+  points = []
+  moves.each do |move|
+    direction = move[0]
+    delta = move[1..].to_i
+    delta.times do
+      pos = pos.move(direction, 1)
+      points << pos
+    end
+  end
+  points
+end
+
+wire1, wire2 = wires(input)
+origin = Point.new(0, 0)
+intersections = (wire1 & wire2).sort do |p1, p2|
+  d1 = p1.manhattan_distance_to origin
+  d2 = p2.manhattan_distance_to origin
+  d1 - d2
+end
+
+pp intersections.first.manhattan_distance_to origin