From eb86963e1a10017e9a28b8309adedf832b9cda48 Mon Sep 17 00:00:00 2001
From: Ben Charlton <ben@spod.cx>
Date: Wed, 16 Dec 2020 21:15:56 +0000
Subject: [PATCH] day 15

---
 15/15.py | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 15/15.py

diff --git a/15/15.py b/15/15.py
new file mode 100644
index 0000000..d22a22c
--- /dev/null
+++ b/15/15.py
@@ -0,0 +1,47 @@
+#!/usr/bin/python3
+
+import sys
+
+for line in sys.stdin:
+    nums = line.rstrip().split(',')
+
+    seen = {}
+    turn = 1
+    last = 0
+    # Load numbers
+    for n in nums:
+        n = int(n)
+        if n in seen:
+            seen[n].append(turn)
+        else:
+            seen[n] = [turn]
+
+        turn += 1
+        last = n
+
+    next = 0
+
+    while turn <= 30000000:
+
+        if last not in seen:
+            next = 0
+        else:
+            a = seen[last]
+            if len(a) == 1:
+                next = 0
+            else:
+                next = a[-1] - a[-2]
+  
+        if next in seen:
+            seen[next].append(turn)
+        else:
+            seen[next] = [turn]
+
+        if turn == 2020:
+            print(1,next)
+
+        turn += 1
+        last = next
+
+    print (2, next)
+