2020/15

y2020/p15.py

+import collections
+import itertools
+import sys
+
+
+text = sys.stdin.read()
+inp = [int(n) for n in text.split(',')][::-1]
+seen = collections.defaultdict(lambda: collections.deque(maxlen=2))
+spoken = None
+for turn in itertools.count(1):
+    if inp:
+        spoken = inp.pop()
+    elif len(seen[spoken]) < 2:
+        spoken = 0
+    else:
+        spoken = seen[spoken][-1] - seen[spoken][-2]
+
+    if turn == 2020:
+        print(spoken)
+    elif turn == 30_000_000:
+        print(spoken)
+        break
+
+    seen[spoken].append(turn)