2024 Day 23

Author: zacklukem

2024/lib/day23.ex

@@ -0,0 +1,79 @@
+defmodule Day23a do
+  def run do
+    File.read!(".input.txt") |> run
+  end
+
+  def run(input) do
+    con = input |> String.split("\n") |> Enum.map(&List.to_tuple(String.split(&1, "-")))
+
+    graph =
+      Graph.new(type: :undirected)
+      |> Graph.add_edges(con)
+
+    Graph.components(graph)
+    |> Enum.flat_map(fn comp ->
+      comp
+      |> Enum.filter(&String.starts_with?(&1, "t"))
+      |> Enum.flat_map(fn x ->
+        n = graph |> Graph.neighbors(x)
+
+        n
+        |> Enum.flat_map(fn y -> n |> Enum.map(&{y, &1}) end)
+        |> Enum.filter(fn {a, b} -> a != b end)
+        |> Enum.filter(fn {a, b} -> Graph.edge(graph, a, b) != nil end)
+        |> Enum.map(fn {a, b} -> MapSet.new([a, b, x]) end)
+      end)
+    end)
+    |> MapSet.new()
+    |> MapSet.size()
+  end
+end
+
+defmodule Day23b do
+  def run do
+    File.read!(".input.txt") |> run
+  end
+
+  def bron_kerbosch(graph) do
+    bron_kerbosch(graph, MapSet.new(), MapSet.new(Graph.vertices(graph)), MapSet.new(), [])
+  end
+
+  def bron_kerbosch(graph, r, p, x, max_cliques) do
+    if MapSet.size(p) == 0 and MapSet.size(x) == 0 do
+      [MapSet.to_list(r) | max_cliques]
+    else
+      p
+      |> Enum.reduce({p, x, max_cliques}, fn v, {p, x, max_cliques} ->
+        n_v = MapSet.new(Graph.neighbors(graph, v))
+
+        max_cliques =
+          bron_kerbosch(
+            graph,
+            MapSet.put(r, v),
+            MapSet.intersection(p, n_v),
+            MapSet.intersection(x, n_v),
+            max_cliques
+          )
+
+        p = p |> MapSet.delete(v)
+        x = x |> MapSet.put(v)
+
+        {p, x, max_cliques}
+      end)
+      |> elem(2)
+    end
+  end
+
+  def run(input) do
+    con = input |> String.split("\n") |> Enum.map(&List.to_tuple(String.split(&1, "-")))
+
+    graph =
+      Graph.new(type: :undirected)
+      |> Graph.add_edges(con)
+
+    bron_kerbosch(graph)
+    |> Enum.max_by(fn comp -> length(comp) end)
+    |> Enum.sort()
+    |> Enum.join(",")
+  end
+end

2024/test/day23_test.exs

@@ -0,0 +1,13 @@
+defmodule Day23Test do
+  use ExUnit.Case
+
+  def example, do: ""
+
+  # test "Part 1 Example" do
+  #   assert Day23a.run(example()) == :todo
+  # end
+
+  #   test "Part 2 Example" do
+  #     assert Day23b.run(example()) == :todo
+  #   end
+end