Add solution code for Day 25 puzzle

Author: akdemironur

25/sample_input

@@ -0,0 +1,13 @@
+jqt: rhn xhk nvd
+rsh: frs pzl lsr
+xhk: hfx
+cmg: qnr nvd lhk bvb
+rhn: xhk bvb hfx
+bvb: xhk hfx
+pzl: lsr hfx nvd
+qnr: nvd
+ntq: jqt hfx bvb xhk
+nvd: lhk
+lsr: lhk
+rzs: qnr cmg lsr rsh
+frs: qnr lhk lsr

25/sol.exs

@@ -0,0 +1,86 @@
+defmodule Day25 do
+  def read_input(file_path) do
+    file_path
+    |> File.read!()
+    |> String.split("\n", trim: true)
+    |> Enum.map(&parse_line/1)
+    |> add_to_graph()
+  end
+
+  def parse_line(line) do
+    [from | rest] = line |> String.split(~r/\ |:/, trim: true)
+    {from, rest}
+  end
+
+  def add_to_graph(l), do: add_to_graph(l, Map.new())
+  def add_to_graph([], graph), do: graph
+
+  def add_to_graph([{from, tos} | rest], graph) do
+    ng = Map.update(graph, from, tos, fn l -> l ++ tos end)
+
+    add_to_graph(
+      rest,
+      tos |> Enum.reduce(ng, fn t, g -> Map.update(g, t, [from], fn l -> [from | l] end) end)
+    )
+  end
+
+  def reach(graph, set) do
+    Enum.reduce(set, MapSet.new(), fn k, acc -> MapSet.new(graph[k]) |> MapSet.union(acc) end)
+    |> MapSet.reject(&MapSet.member?(set, &1))
+  end
+
+  def number_of_outer_connections(graph, set) do
+    r = reach(graph, set)
+
+    Enum.reduce(r, 0, fn v, acc ->
+      (graph[v] |> Enum.filter(&MapSet.member?(set, &1)) |> length()) + acc
+    end)
+  end
+
+  def put_vertex(graph, {vs, es}, v) do
+    new_es =
+      ((es |> Enum.reject(fn {_, t} -> t == v end)) ++
+         (graph[v] |> Enum.reject(&MapSet.member?(vs, &1)) |> Enum.map(&{v, &1})))
+      |> MapSet.new()
+
+    new_vs = MapSet.put(vs, v)
+
+    {new_vs, new_es}
+  end
+
+  def solve(graph) do
+    first = graph |> Enum.at(0) |> elem(0)
+    first_con = graph[first]
+    initial_edges = first_con |> Enum.map(&{first, &1}) |> MapSet.new()
+
+    solve(
+      graph,
+      [{MapSet.new([first]), initial_edges}],
+      MapSet.new()
+    )
+  end
+
+  def solve(graph, [{v, e} | sets], seen) do
+    new_seen = seen |> MapSet.put(v)
+
+    case MapSet.size(e) do
+      3 ->
+        (map_size(graph) - MapSet.size(v)) * MapSet.size(v)
+
+      _ ->
+        r = e |> Enum.map(&elem(&1, 1)) |> Enum.dedup()
+
+        new_s =
+          r
+          |> Enum.map(&put_vertex(graph, {v, e}, &1))
+          |> Enum.reject(&MapSet.member?(new_seen, elem(&1, 0)))
+          |> Enum.sort_by(&MapSet.size(MapSet.difference(elem(&1, 1), e)))
+
+        solve(graph, new_s ++ sets, new_seen)
+    end
+  end
+
+  def partA(file_path) do
+    file_path |> read_input() |> solve()
+  end
+end