1 files changed, 42 insertions, 0 deletions
diff --git a/20/py/d15.py b/20/py/d15.py
new file mode 100644
index 0000000..8723a28
--- /dev/null
+++ b/20/py/d15.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+import aoc20
+import sys
+
+
+def pt1(_in):
+    nums = [int(n) for n in _in[0].split(",")]
+    prev = {n: i for i, n in enumerate(nums)}
+    while len(nums) < 2020:
+        cur = nums[-1]
+        if cur not in prev:
+            nums.append(0)
+            prev[cur] = len(nums) - 2
+        else:
+            nums.append(len(nums) - 1 - prev[cur])
+            prev[cur] = len(nums) - 2
+    return nums[2019]
+
+
+def pt2(_in):
+    nums = [int(n) for n in _in[0].split(",")]
+    amount = 3
+    cur = nums[-1]
+    prev = {n: i for i, n in enumerate(nums)}
+    while amount < 30000000:
+        if amount % 300000 == 0:
+            print(amount // 300000)
+        if cur not in prev:
+            new = 0
+            prev[cur] = amount - 1
+        else:
+            new = amount - 1 - prev[cur]
+            prev[cur] = amount - 1
+        cur = new
+        amount += 1
+    return cur
+
+
+if __name__ == "__main__":
+    input = aoc20.read_input(sys.argv[1:], 15)
+    print(pt1(input))
+    print(pt2(input))