diff --git a/2018/day9-input b/2018/day9-input
new file mode 100644
index 0000000..f2c7360
--- /dev/null
+++ b/2018/day9-input
@@ -0,0 +1 @@
+428 players; last marble is worth 72061 points
diff --git a/2018/day9.py b/2018/day9.py
new file mode 100644
index 0000000..79a3b12
--- /dev/null
+++ b/2018/day9.py
@@ -0,0 +1,26 @@
+import numpy as np
+from itertools import cycle
+from blist import blist  # Regular lists are far too slow for Part 2, as are numpy arrays.
+
+with open('day9-input', 'r') as file:
+  data = [l.strip('\n') for l in file][0].split()
+players = int(data[0])
+last_marble = int(data[-2])
+
+
+def find_winning_score(players, last_marble):
+  marbles = blist([0])
+  scores = np.zeros(players, dtype=np.int64)
+  current_marble = 0
+  for marble, player in zip(range(1, last_marble+1), cycle(range(players))):
+    if marble % 23 == 0:
+      current_marble = (current_marble-7) % len(marbles)
+      scores[player] += marble + marbles.pop(current_marble)
+    else:
+      current_marble = (current_marble+2) % len(marbles)
+      marbles.insert(current_marble, marble)
+  return max(scores)
+
+
+print(find_winning_score(players, last_marble))  # Part 1
+print(find_winning_score(players, last_marble*100))  # Part 2