From 12e2fd4d7497972a63ba0bc341db3fa59b6d45b5 Mon Sep 17 00:00:00 2001
From: Luke Hubmayer-Werner <mongoose41@gmail.com>
Date: Tue, 15 Dec 2020 16:48:56 +1030
Subject: [PATCH] 2020 day 15

---
 2020/day15.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 2020/day15.py

diff --git a/2020/day15.py b/2020/day15.py
new file mode 100644
index 0000000..9aa98d0
--- /dev/null
+++ b/2020/day15.py
@@ -0,0 +1,17 @@
+def play_game(data, until):
+  last_indices = {v:i for i,v in enumerate(data[:-1])}
+  last = data[-1]
+  for i in range(len(data), until):
+    if last in last_indices:
+      n = i-last_indices[last]-1
+      last_indices[last] = i-1
+      last = n
+    else:
+      last_indices[last] = i-1
+      last = 0
+  return last
+
+input = [int(i) for i in '10,16,6,0,1,17'.split(',')]
+
+print(f'Part 1: 2020th number is {play_game(input, 2020)}')
+print(f'Part 2: 30000000th number is {play_game(input, 30000000)}')