Alternative

Author: r0f1

README.md

@@ -16,7 +16,7 @@
 |[12](https://adventofcode.com/2020/day/12)|Rain Risk|[py](/day12/main.py)|
 |[13](https://adventofcode.com/2020/day/13)|Shuttle Search|[py](/day13/main.py)|
 |[14](https://adventofcode.com/2020/day/14)|Docking Data|[py](/day14/main.py)|
-|[15](https://adventofcode.com/2020/day/15)|Rambunctious Recitation|[py](/day15/main.py)|
+|[15](https://adventofcode.com/2020/day/15)|Rambunctious Recitation|[py](/day15/main.py), [alt](/day15/alt.py)|
 |[16](https://adventofcode.com/2020/day/16)|-|-|
 |[17](https://adventofcode.com/2020/day/17)|-|-|
 |[18](https://adventofcode.com/2020/day/18)|-|-|

day15/alt.py

@@ -0,0 +1,10 @@
+def solve(numbers, until):
+    memory = {n: i+1 for i, n in enumerate(numbers[:-1])}
+    for i in range(len(numbers), until):
+        numbers.append(i - memory.get(numbers[-1], i))
+        memory[numbers[-2]] = i
+    return numbers[-1]
+
+numbers = [int(n) for n in "12,1,16,3,11,0".split(",")]
+print(solve(numbers, 2020))
+print(solve(numbers, 30000000))