diff --git a/2021/ruby/day_17.rb b/2021/ruby/day_17.rb
new file mode 100644
index 0000000..2cd1645
--- /dev/null
+++ b/2021/ruby/day_17.rb
@@ -0,0 +1,33 @@
+class Probe
+  def initialize(velocity, target)
+    @velocity, @target = velocity, target
+  end
+
+  def each
+    return enum_for(__method__) unless block_given?
+
+    pos = [0,0]
+    velocity = @velocity.clone
+
+    loop do
+      yield pos
+
+      return if @target.zip(pos).all? { _1.cover?(_2) }
+
+      pos = pos.zip(velocity).map { _1.sum }
+      velocity[0] -= 1 if velocity[0] > 0
+      velocity[1] -= 1
+
+      return if pos[0] > @target[0].end
+      return if pos[1] < @target[1].begin
+    end
+  end
+end
+
+input = ARGF.read.scan(/x=(.+), y=(.+)/)
+target = input[0].map { eval(_1) }
+
+haystack = (0..256).flat_map {|x| (-256..256).map {|y| [x, y] }}
+haystack.select! {|v| Probe.new(v, target).each.any? {|pos| target.zip(pos).all? { _1.cover?(_2) }}}
+# p haystack.map {|v| Probe.new(v, target).each.map { _2 }.max }.max
+p haystack.count