Solve 2020 day 15

2020/15_numbersgame.py

@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+def gen(start):
+    yield from start
+    spoken = {n: i for i, n in enumerate(start)}
+    i = len(start)
+    num = 0
+    while True:
+        yield num
+        nextnum = i - spoken.get(num, i)
+        spoken[num] = i
+        num = nextnum
+        i += 1
+
+def nth(start, n):
+    return next(num for i, num in enumerate(gen(start)) if i == n - 1)
+
+start = [13, 0, 10, 12, 1, 5, 8]
+print(nth(start, 2020))
+print(nth(start, 30000000))