diff --git a/2017/ruby/day_14.rb b/2017/ruby/day_14.rb
new file mode 100644
index 0000000..b696929
--- /dev/null
+++ b/2017/ruby/day_14.rb
@@ -0,0 +1,52 @@
+input = ARGF.read.strip
+
+def knot_hash(input)
+  list = (0..255).to_a
+  current = 0
+  lengths = input.split(//).map(&:ord)
+  lengths.concat([17, 31, 73, 47, 23])
+  skip = 0
+  64.times do
+    lengths.each do |length|
+      list[0, length] = list[0, length].reverse
+      list = list.rotate(length + skip)
+      current += length + skip
+      current %= list.size
+      skip += 1
+    end
+  end
+
+  list = list.rotate(list.size - current)
+  dense = list.each_slice(16).map {|slice| slice.inject(&:^) }
+  hex = dense.map {|n| n.to_s(16).rjust(2, ?0) }.join
+  hex.hex.to_s(2).rjust(128, ?0)
+end
+
+# p (0..127).map {|i| "#{input}-#{i}" }.map {|row| knot_hash(row) }.join.split(//).select {|c| c == ?1 }.count
+
+# input = "flqrgnkx"
+grid = (0..127).map {|i| "#{input}-#{i}" }.map {|row| knot_hash(row).split(//) }
+
+regions = 0
+queue = []
+(0..127).each do |y|
+  (0..127).each do |x|
+    if grid[y][x] == ?1
+      regions += 1
+      grid[y][x] = ?0
+      queue << [x, y]
+      until queue.empty?
+        xx,yy = queue.shift
+        [[0, 1], [0, -1], [1, 0], [-1, 0]].each do |dx, dy|
+          xxx = xx + dx
+          yyy = yy + dy
+          if (0..127).cover?(xxx) && (0..127).cover?(yyy) && grid[yyy][xxx] == ?1
+            grid[yyy][xxx] = ?0
+            queue << [xxx, yyy]
+          end
+        end
+      end
+    end
+  end
+end
+p regions