Solve 2020 day 15

2020/d15.py

@@ -0,0 +1,22 @@
+from lib import get_data, str_to_ints
+from collections import defaultdict
+
+data = get_data(__file__)
+
+for limit in [2021, 30000001]:
+    xs = list(reversed(str_to_ints(data)))
+    spoken = defaultdict(list)
+    recent = None
+    for turn in range(1, limit):
+        if len(xs) > 0:
+            recent = xs.pop()
+            spoken[recent].append(turn)
+        else:
+            if recent in spoken and len(spoken[recent]) == 1:
+                recent = 0
+            elif recent in spoken:
+                recent = spoken[recent][-1] - spoken[recent][-2]
+            else:
+                recent = 0
+            spoken[recent].append(turn)
+    print(recent)