diff --git a/2018/ruby/day_17.rb b/2018/ruby/day_17.rb
new file mode 100644
index 0000000..c733ed1
--- /dev/null
+++ b/2018/ruby/day_17.rb
@@ -0,0 +1,75 @@
+require "set"
+
+require "minitest"
+require "minitest/pride"
+
+class Slice
+  def self.parse(s)
+    clay = Set.new
+    s.scan(/^(x|y)=(\d+), (?:x|y)=(\d+)..(\d+)$/m).each do |xy, i, min, max|
+      i, min, max = [i, min, max].map(&:to_i)
+      clay.merge((min..max).map {|j| xy == ?x ? [j, i] : [i, j] })
+    end
+    new(clay)
+  end
+
+  def initialize(clay)
+    @clay = clay
+  end
+
+  def to_s
+    min_x, max_x = @clay.map(&:last).minmax
+    min_y, max_y = @clay.map(&:first).minmax
+    min_y = [0, min_y].min
+    (min_y..max_y).map {|y|
+      (min_x-1..max_x+1).map {|x|
+        if [x, y] == [500, 0]
+          ?+
+        else
+          @clay.include?([y, x]) ? ?# : ?.
+        end
+      }.join
+    }.join(?\n)
+  end
+end
+
+class TestSlice < Minitest::Test
+  def test_parse_to_s
+    slice = Slice.parse(<<~SLICE)
+      x=495, y=2..7
+      y=7, x=495..501
+      x=501, y=3..7
+      x=498, y=2..4
+      x=506, y=1..2
+      x=498, y=10..13
+      x=504, y=10..13
+      y=13, x=498..504
+    SLICE
+
+    assert_equal <<~SLICE.chomp, slice.to_s
+      ......+.......
+      ............#.
+      .#..#.......#.
+      .#..#..#......
+      .#..#..#......
+      .#.....#......
+      .#.....#......
+      .#######......
+      ..............
+      ..............
+      ....#.....#...
+      ....#.....#...
+      ....#.....#...
+      ....#######...
+    SLICE
+  end
+end
+
+def solve(input)
+end
+
+if __FILE__ == $0
+  require "minitest/autorun" and exit if ENV["TEST"]
+
+  puts solve(ARGF.read)
+end