From c1125d6ede53a691f94f6f7dc8bdb3d03da0f5a9 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 13
---
2015/README.md | 13 +++---
2015/lib/2015/13.ex | 100 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 107 insertions(+), 6 deletions(-)
create mode 100644 2015/lib/2015/13.ex
diff --git a/2015/README.md b/2015/README.md
index 32fbaa1..c6c37e7 100644
--- a/2015/README.md
+++ b/2015/README.md
@@ -12,12 +12,12 @@
```
</details>
-| S | M | T | W | T | F | S |
-| :-: | :-: | :-: | :-: | :-: | :-: | :-: |
-| | | [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 | |
+| S | M | T | W | T | F | S |
+| :--: | :-: | :-: | :-: | :-: | :-: | :-: |
+| | | [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 | |
[1]: ./lib/2015/1.ex
[2]: ./lib/2015/2.ex
@@ -31,3 +31,4 @@
[10]: ./lib/2015/10.ex
[11]: ./lib/2015/11.ex
[12]: ./lib/2015/12.ex
+[13]: ./lib/2015/13.ex
diff --git a/2015/lib/2015/13.ex b/2015/lib/2015/13.ex
new file mode 100644
index 0000000..1c7d299
--- /dev/null
+++ b/2015/lib/2015/13.ex
@@ -0,0 +1,100 @@
+import AOC
+
+aoc 2015, 13 do
+ import NimbleParsec
+
+ def p1 do
+ {guests, edges} = parse_input()
+
+ permutations(guests)
+ |> Enum.map(&happiness(edges, &1))
+ |> Enum.max()
+ end
+
+ def p2 do
+ {guests, edges} = parse_input()
+
+ guests = guests ++ ["Zach"]
+
+ permutations(guests)
+ |> Enum.map(&happiness(edges, &1))
+ |> Enum.max()
+ end
+
+ defparsec(
+ :fact_parsec,
+ ascii_string([?a..?z, ?A..?Z], min: 1)
+ |> ignore(string(" would "))
+ |> choice([
+ string("gain"),
+ string("lose")
+ ])
+ |> ignore(string(" "))
+ |> integer(min: 1)
+ |> ignore(string(" happiness units by sitting next to "))
+ |> ascii_string([?a..?z, ?A..?Z], min: 1)
+ |> ignore(string("."))
+ )
+
+ def parse_fact(str) do
+ {:ok, [left, sign, amount, right], _, _, _, _} = fact_parsec(str)
+
+ {{left, right}, edge_value(sign, amount)}
+ end
+
+ def edge_value("gain", v), do: v
+ def edge_value("lose", v), do: 0 - v
+
+ def sort({a, b} = p) when a > b, do: swap(p)
+ def sort(p), do: p
+ def swap({a, b}), do: {b, a}
+
+ def parse_input() do
+ edges =
+ input_stream()
+ |> Stream.map(&parse_fact/1)
+ |> Enum.into(%{})
+
+ guests =
+ edges
+ |> Map.keys()
+ |> Enum.reduce(MapSet.new(), fn {a, b}, acc -> acc |> MapSet.put(a) |> MapSet.put(b) end)
+
+ edges =
+ for {pair, weight} <- edges, reduce: %{} do
+ acc ->
+ sorted = sort(pair)
+
+ if Map.has_key?(acc, sorted) do
+ acc
+ else
+ reverse = swap(pair)
+ Map.put(acc, sorted, weight + Map.get(edges, reverse))
+ end
+ end
+
+ guests = Enum.to_list(guests)
+
+ {guests, edges}
+ end
+
+ def permutations([]), do: [[]]
+
+ def permutations(xs) do
+ for h <- xs, t <- permutations(xs -- [h]), do: [h | t]
+ end
+
+ def happiness(edges, [a | _] = xs) do
+ happiness(edges, xs, a, 0)
+ end
+
+ def happiness(edges, [t], h, acc) do
+ edge = Map.get(edges, sort({h, t}), 0)
+ edge + acc
+ end
+
+ def happiness(edges, [a, b | rest], h, acc) do
+ edge = Map.get(edges, sort({a, b}), 0)
+ happiness(edges, [b | rest], h, acc + edge)
+ end
+end