Day 11.

11.py

@@ -0,0 +1,35 @@
+import collections
+
+reductions = [
+    # Simplifications
+    [ 'n', 'se', 'ne'],
+    [ 'n', 'sw', 'nw'],
+    [ 's', 'ne', 'se'],
+    [ 's', 'nw', 'sw'],
+    ['sw', 'se',  's'],
+    ['nw', 'ne',  'n'],
+    # Opposites
+    [ 'n',  's', '--'],
+    ['sw', 'ne', '--'],
+    ['nw', 'se', '--'],
+]
+
+
+def distance(steps):
+    counts = collections.defaultdict(lambda: 0, collections.Counter(steps))
+    last_counts = dict()
+    while counts != last_counts:
+        last_counts = dict(counts)
+        for a, b, result in reductions:
+            count = min(counts[a], counts[b])
+            counts[a] -= count
+            counts[b] -= count
+            counts[result] += count
+    counts['--'] = 0
+    return sum(counts.values())
+
+
+with open('data/11.txt', 'r') as file:
+    steps = file.readline().strip().split(',')
+    print(f'Part one: {distance(steps)}')
+    print(f'Part two: {max(distance(steps[:i]) for i in range(len(steps)))}')