wip

examples/18.txt

@@ -0,0 +1,14 @@
+R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)

lib/days/18.rb

@@ -0,0 +1,105 @@
+class Day18
+
+  Point = Data.define(:x, :y) do
+    def at?(x, y)
+      self.x == x && self.y == y
+    end
+
+    def neighbors
+      [
+        Point.new(x - 1, y),
+        Point.new(x + 1, y),
+        Point.new(x, y - 1),
+        Point.new(x, y + 1)
+      ].reject { |p| p.x.negative? || p.y.negative? }
+    end
+  end
+
+  GridInfo = Data.define(:min_x, :max_x, :min_y, :max_y) do
+    def valid?(x, y)
+      x >= min_x && x <= max_x && y >= min_y && y < max_y
+    end
+
+    def size
+      (max_x - min_x + 1) * (max_y - min_y + 1)
+    end
+  end
+
+  UP = 'U'
+  DOWN = 'D'
+  LEFT = 'L'
+  RIGHT = 'R'
+
+  def part1(input)
+    trench = Set.new
+    current = Point.new(0, 0)
+    trench.add(current)
+
+    input.split("\n").each do |line|
+      direction, count, = line.split
+      count = count.to_i
+
+      case direction
+      when UP
+        count.times do
+          current = Point.new(current.x, current.y - 1)
+          trench.add current
+        end
+      when DOWN
+        count.times do
+          current = Point.new(current.x, current.y + 1)
+          trench.add current
+        end
+      when LEFT
+        count.times do
+          current = Point.new(current.x - 1, current.y)
+          trench.add current
+        end
+      when RIGHT
+        count.times do
+          current = Point.new(current.x + 1, current.y)
+          trench.add current
+        end
+      end
+    end
+
+    info = GridInfo.new(
+      trench.map(&:x).min,
+      trench.map(&:x).max,
+      trench.map(&:y).min,
+      trench.map(&:y).max
+    )
+
+    outside = Set.new
+
+    (info.min_x..info.max_x).each do |x|
+      (info.min_y..info.max_y).each do |y|
+        point = Point.new(x, y)
+
+        if (x == info.min_x || y == info.min_y || x == info.max_x || y == info.max_y) && !trench.include?(point)
+          outside.add(point)
+        end
+      end
+    end
+
+    outside.to_a.each do |point|
+      check_neighbors(point, trench, outside, info)
+    end
+
+    info.size - outside.size
+  end
+
+  def check_neighbors(point, trench, outside, info)
+    point.neighbors.each do |p|
+      next if trench.include?(p) || outside.include?(p) || !info.valid?(p.x, p.y)
+
+      outside.add(p)
+      check_neighbors(p, trench, outside, info)
+    end
+  end
+
+  def part2(input)
+    'TODO'
+  end
+
+end

test/18_test.rb

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+require 'minitest/autorun'
+require 'minitest/pride'
+require_relative '../app'
+
+class TestDay18 < Minitest::Test
+  def setup
+    @data = File.read(File.join(APP_ROOT, 'examples', '18.txt')).rstrip
+    @day = Day18.new
+  end
+
+  def test_part1
+    assert_equal @day.part1(@data), 62
+  end
+
+  def test_part2
+    assert_equal @day.part2(@data), ''
+  end
+end