From 8bd3f02d6e51eea12cb80457d2d17910948cde28 Mon Sep 17 00:00:00 2001
From: Sloane Perrault <sloane.perrault@gmail.com>
Date: Wed, 21 Sep 2022 09:19:54 -0400
Subject: [PATCH] 2021 day 20
---
2021/README.md | 4 +-
2021/lib/2021/20.ex | 104 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 106 insertions(+), 2 deletions(-)
create mode 100644 2021/lib/2021/20.ex
diff --git a/2021/README.md b/2021/README.md
index a82dfd9..3aa8c30 100644
--- a/2021/README.md
+++ b/2021/README.md
@@ -17,7 +17,7 @@
| | | | [1] | [2] | [3] | [4] |
| [5] | [6] | [7] | [8] | [9] | [10] | [11]|
| [12]| [13]| [14]| [15] | [16] | [17] | [18] |
-| [19] | 20 | [21] | 22 | 23 | 24 | 25 |
+| [19] | [20] | [21] | 22 | 23 | 24 | 25 |
<!-- links -->
@@ -40,5 +40,5 @@
[17]: ./lib/2021/17.ex
[18]: ./lib/2021/18.ex
[19]: ./lib/2021/19.ex
-
+[20]: ./lib/2021/20.ex
[21]: ./lib/2021/21.ex
diff --git a/2021/lib/2021/20.ex b/2021/lib/2021/20.ex
new file mode 100644
index 0000000..90c914e
--- /dev/null
+++ b/2021/lib/2021/20.ex
@@ -0,0 +1,104 @@
+import AOC
+
+aoc 2021, 20 do
+ import Integer, only: [is_even: 1]
+
+ def p1 do
+ {algorithm, source_image} = input()
+
+ enhance(source_image, algorithm, 2)
+ |> Map.values()
+ |> Enum.count(&(&1))
+ end
+
+ def p2 do
+ {algorithm, source_image} = input()
+
+ enhance(source_image, algorithm, 50)
+ |> Map.values()
+ |> Enum.count(&(&1))
+ end
+
+ def enhance(image, algorithm, to_iteration, iteration \\ 0)
+ def enhance(image, _algorithm, iteration, iteration), do: image
+
+ def enhance(image, algorithm, to_iteration, iteration) do
+ infinite_expanse = if is_even(iteration), do: Map.get(algorithm, 511), else: Map.get(algorithm, 0)
+
+ {i_range, j_range} = bounds(image)
+
+ for i <- i_range, j <- j_range, into: %{} do
+ {{i, j}, Map.get(algorithm, algorithm_idx(image, {i, j}, infinite_expanse))}
+ end
+ |> enhance(algorithm, to_iteration, iteration + 1)
+ end
+
+ def bounds(image) do
+ {{i_min, j_min}, {i_max, j_max}} =
+ image
+ |> Map.keys()
+ |> Enum.min_max()
+
+ {Range.new(i_min - 2, i_max + 2), Range.new(j_min - 2, j_max + 2)}
+ end
+
+ def algorithm_idx(image, {i, j}, infinite_expanse) do
+ [
+ {i - 1, j - 1},
+ {i - 1, j},
+ {i - 1, j + 1},
+ {i, j - 1},
+ {i, j},
+ {i, j + 1},
+ {i + 1, j - 1},
+ {i + 1, j},
+ {i + 1, j + 1}
+ ]
+ |> Enum.map(&Map.get(image, &1, infinite_expanse))
+ |> Enum.map(fn
+ true -> 1
+ false -> 0
+ end)
+ |> Integer.undigits(2)
+ end
+
+
+ def input() do
+ [unparsed_algorithm, unparsed_source_image] =
+ input_string()
+ |> String.split("\n\n", trim: true)
+
+ algorithm =
+ unparsed_algorithm
+ |> String.split("", trim: true)
+ |> Enum.with_index()
+ |> Enum.map(fn
+ {"#", i} -> {i, true}
+ {".", i} -> {i, false}
+ end)
+ |> Enum.into(%{})
+
+ source_image =
+ unparsed_source_image
+ |> String.split("\n", trim: true)
+ |> Enum.map(fn line ->
+ line
+ |> String.split("", trim: true)
+ |> Enum.map(fn
+ "#" -> true
+ "." -> false
+ end)
+ |> Enum.with_index()
+ end)
+ |> Enum.with_index()
+ |> then(&for(
+ {row, i} <- &1,
+ {cell, j} <- row,
+ into: %{},
+ do: {{i, j}, cell}
+ ))
+
+
+ {algorithm, source_image}
+ end
+end