From 8d8da8d6a393213a277c0b29b7e4485e1f2c00c2 Mon Sep 17 00:00:00 2001
From: Sloane Perrault <sloane.perrault@gmail.com>
Date: Wed, 21 Sep 2022 09:19:53 -0400
Subject: [PATCH] solve 2015 day 18
---
2015/README.md | 3 +-
2015/lib/2015/18.ex | 105 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 107 insertions(+), 1 deletion(-)
create mode 100644 2015/lib/2015/18.ex
diff --git a/2015/README.md b/2015/README.md
index 0ed2f5b..d8143d1 100644
--- a/2015/README.md
+++ b/2015/README.md
@@ -16,7 +16,7 @@
| :--: | :--: | :-: | :-: | :-: | :-: | :-: |
| | | [1] | [2] | [3] | [4] | [5] |
| [6] | [7] | [8] | [9] | [10] | [11] | [12] |
-| [13] | [14] | [15] | [16]| [17] | 18 | 19 |
+| [13] | [14] | [15] | [16]| [17] | [18] | 19 |
| 20 | 21 | 22 | 23 | 24 | 25 | |
[1]: ./lib/2015/1.ex
@@ -36,3 +36,4 @@
[15]: ./lib/2015/15.ex
[16]: ./lib/2015/16.ex
[17]: ./lib/2015/17.ex
+[18]: ./lib/2015/18.ex
diff --git a/2015/lib/2015/18.ex b/2015/lib/2015/18.ex
new file mode 100644
index 0000000..1dcf46c
--- /dev/null
+++ b/2015/lib/2015/18.ex
@@ -0,0 +1,105 @@
+import AOC
+
+aoc 2015, 18 do
+ def input() do
+ lists =
+ input_string()
+ |> String.split("\n", trim: true)
+ |> Enum.map(fn line ->
+ line
+ |> String.split("", trim: true)
+ |> Enum.map(&decode_state/1)
+ |> Enum.with_index(1)
+ end)
+ |> Enum.with_index(1)
+
+ for {row, i} <- lists, {cell, j} <- row, into: %{} do
+ {{i, j}, cell}
+ end
+ end
+
+ def decode_state("#"), do: :on
+ def decode_state("."), do: :off
+
+ def encode_state(:on), do: "#"
+ def encode_state(:off), do: :off
+
+ def n({i, j}), do: {i - 1, j}
+ def e({i, j}), do: {i, j + 1}
+ def s({i, j}), do: {i + 1, j}
+ def w({i, j}), do: {i, j - 1}
+ def ne(pos), do: pos |> n() |> e()
+ def se(pos), do: pos |> s() |> e()
+ def sw(pos), do: pos |> s() |> w()
+ def nw(pos), do: pos |> n() |> w()
+
+ def neighbors(map, pos) do
+ [&n/1, &ne/1, &e/1, &se/1, &s/1, &sw/1, &w/1, &nw/1]
+ |> Enum.map(&apply(&1, [pos]))
+ |> Enum.map(&Map.get(map, &1, :off))
+ |> Enum.frequencies()
+ end
+
+ def tick(map) do
+ for {pos, cell} <- map, into: %{} do
+ next_cell =
+ case {cell, neighbors(map, pos)} do
+ {:on, %{on: on}} when on in [2, 3] -> :on
+ {:on, _} -> :off
+ {:off, %{on: 3}} -> :on
+ {:off, _} -> :off
+ end
+
+ {pos, next_cell}
+ end
+ end
+
+ def tick_with_corners_on(map) do
+ for {pos, cell} <- map, into: %{} do
+ if pos in [{1, 1}, {1, 100}, {100, 1}, {100, 100}] do
+ {pos, :on}
+ else
+ next_cell =
+ case {cell, neighbors(map, pos)} do
+ {:on, %{on: on}} when on in [2, 3] -> :on
+ {:on, _} -> :off
+ {:off, %{on: 3}} -> :on
+ {:off, _} -> :off
+ end
+
+ {pos, next_cell}
+ end
+ end
+ end
+
+ def p1 do
+ start = input()
+
+ finish =
+ for _ <- 1..100, reduce: start do
+ curr -> tick(curr)
+ end
+
+ finish
+ |> Map.values()
+ |> Enum.count(&(&1 == :on))
+ end
+
+ def p2 do
+ start =
+ input()
+ |> Map.put({1, 1}, :on)
+ |> Map.put({1, 100}, :on)
+ |> Map.put({100, 1}, :on)
+ |> Map.put({100, 100}, :on)
+
+ finish =
+ for _ <- 1..100, reduce: start do
+ curr -> tick_with_corners_on(curr)
+ end
+
+ finish
+ |> Map.values()
+ |> Enum.count(&(&1 == :on))
+ end
+end