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hauleth.dev
1<!-- vim:set ft=markdown: -->
2
3<!-- livebook:{"persist_outputs":true} -->
4
5# Day 13
6
7```elixir
8[input, folds] =
9 File.read!("day13.txt")
10 |> String.trim()
11 |> String.split("\n\n")
12
13input =
14 input
15 |> String.split("\n")
16 |> Enum.map(fn line ->
17 [x, y] = String.split(line, ",")
18
19 {String.to_integer(x), String.to_integer(y)}
20 end)
21 |> MapSet.new()
22
23folds =
24 folds
25 |> String.split("\n")
26 |> Enum.map(fn
27 "fold along " <> <<c>> <> "=" <> rest ->
28 {String.to_atom(<<c>>), String.to_integer(rest)}
29 end)
30
31defmodule Day13 do
32 def fold({orientation, pos}, set) do
33 Enum.reduce(set, MapSet.new(), fn point, acc ->
34 new_point = folded_coords(orientation, pos, point)
35
36 MapSet.put(acc, new_point)
37 end)
38 end
39
40 defp folded_coords(:x, col, {x, y}) when x > col, do: {abs(2 * col - x), y}
41 defp folded_coords(:y, row, {x, y}) when y > row, do: {x, abs(2 * row - y)}
42 defp folded_coords(_, _, point), do: point
43
44 def draw(set) do
45 set
46 |> Enum.group_by(&elem(&1, 1))
47 |> Enum.sort()
48 |> Enum.map(fn {_, points} ->
49 points
50 |> Enum.map(&elem(&1, 0))
51 |> Enum.sort()
52 |> Enum.chunk_every(2, 1)
53 |> Enum.map(fn
54 [a, b] -> b - a
55 _ -> 0
56 end)
57 |> Enum.map(&String.pad_trailing("█", &1, " "))
58 end)
59 |> Enum.join("\n")
60 end
61end
62```
63
64```output
65{:module, Day13, <<70, 79, 82, 49, 0, 0, 13, ...>>, {:draw, 1}}
66```
67
68## Task 1
69
70```elixir
71Day13.fold(hd(folds), input) |> MapSet.size()
72```
73
74```output
75802
76```
77
78## Task 2
79
80```elixir
81Enum.reduce(folds, input, &Day13.fold/2)
82|> Day13.draw()
83|> IO.puts()
84```
85
86```output
87███ █ █ █ █ ████ ████ ██ █ █ ███
88█ █ █ █ █ █ █ █ █ █ █ █ █ █
89█ █ ██ ████ ███ █ █ █ █ ███
90███ █ █ █ █ █ █ █ ██ █ █ █ █
91█ █ █ █ █ █ █ █ █ █ █ █ █ █
92█ █ █ █ █ █ █ ████ ███ ██ ███
93```
94
95```output
96:ok
97```
98