From 572dc93c20caa9ac216bdf31e641164fb99dab87 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Tue, 3 Dec 2019 09:43:40 -0800
Subject: [PATCH] 2019: Day 2 Part 2

---
 2019/day3/part2.rb | 107 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 2019/day3/part2.rb

diff --git a/2019/day3/part2.rb b/2019/day3/part2.rb
new file mode 100644
index 0000000..d522d75
--- /dev/null
+++ b/2019/day3/part2.rb
@@ -0,0 +1,107 @@
+# 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)
+
+def times(wire)
+  by_time = {}
+  wire.each_with_index do |p, t|
+    by_time[p] = t + 1 unless by_time.key? p
+  end
+  by_time
+end
+
+t1 = times(wire1)
+t2 = times(wire2)
+
+intersections = t1.keys & t2.keys
+
+intersection_times = {}
+intersections.each do |p|
+  intersection_times[p] = t1[p] + t2[p]
+end
+
+sorted_intersections = intersection_times.each_pair.sort_by { |_, t| t }
+pp sorted_intersections
+
+pp sorted_intersections.first