2022 Day 8 - even though I said I'd quit yesterday...

2022/README.md

@@ -2,7 +2,7 @@
 
 My (attempted) solutions to [Advent of Code 2022](https://adventofcode.com/2022) in Elixir.
 
-<img width="866" alt="image" src="https://user-images.githubusercontent.com/498229/206192088-8193678c-ff03-419b-b733-9db17131a9d1.png">
+<img width="866" alt="image" src="https://user-images.githubusercontent.com/498229/206484136-257f8811-6aae-4316-9c7e-5aa9eb9dcfa7.png">
 
 ## Running:
 

2022/day8.exs

@@ -0,0 +1,130 @@
+defmodule Day8 do
+  defmodule Tree do
+    defstruct height: nil, visible: false, score: []
+  end
+
+  def part1({{max_x, max_y}, trees}) do
+    trees
+    |> look_in_direction(0..max_y, 0..max_x, false)
+    |> look_in_direction(0..max_x, 0..max_y, true)
+    |> look_in_direction(0..max_y, max_x..0, false)
+    |> look_in_direction(0..max_x, max_y..0, true)
+    |> Enum.count(&match?({_coord, %Tree{visible: true}}, &1))
+  end
+
+  defp look_in_direction(trees, outer_range, inner_range, flip_xy?) do
+    Enum.reduce(outer_range, trees, fn y, trees ->
+      {_height, trees} =
+        Enum.reduce_while(inner_range, {_height = -1, trees}, fn
+          _x, {9, trees} ->
+            {:halt, {9, trees}}
+
+          x, {height, trees} ->
+            coord = if flip_xy?, do: {y, x}, else: {x, y}
+            tree = trees[coord]
+
+            if tree.height > height do
+              {:cont, {tree.height, Map.replace(trees, coord, %Tree{tree | visible: true})}}
+            else
+              {:cont, {height, trees}}
+            end
+        end)
+
+      trees
+    end)
+  end
+
+  def part2({{max_x, max_y}, trees}) do
+    trees
+    |> count_viewing_distance(0..max_y, 0..max_x, false)
+    |> count_viewing_distance(0..max_x, 0..max_y, true)
+    |> count_viewing_distance(0..max_y, max_x..0, false)
+    |> count_viewing_distance(0..max_x, max_y..0, true)
+    |> Enum.map(fn {_coord, %Tree{score: score}} -> Enum.reduce(score, &Kernel.*/2) end)
+    |> Enum.max()
+  end
+
+  defp count_viewing_distance(trees, outer_range, inner_range, flip_xy?) do
+    Enum.reduce(outer_range, trees, fn y, trees ->
+      {_scoring, trees} =
+        Enum.reduce(inner_range, {_scoring = [], trees}, fn
+          x, {scoring, trees} ->
+            coord = if flip_xy?, do: {y, x}, else: {x, y}
+            tree = trees[coord]
+
+            {scoring, trees} =
+              Enum.reduce(scoring, {[], trees}, fn {coord, scoring_tree}, {scoring, trees} ->
+                %Tree{score: [score | scores]} = scoring_tree
+                scoring_tree = %Tree{scoring_tree | score: [score + 1 | scores]}
+                trees = Map.replace(trees, coord, scoring_tree)
+
+                if scoring_tree.height <= tree.height do
+                  {scoring, trees}
+                else
+                  {[{coord, scoring_tree} | scoring], trees}
+                end
+              end)
+
+            tree = %Tree{tree | score: [0 | tree.score]}
+            {[{coord, tree} | scoring], Map.replace(trees, coord, tree)}
+        end)
+
+      trees
+    end)
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      grid =
+        input
+        |> String.trim()
+        |> String.split("\n")
+        |> Enum.map(&String.graphemes/1)
+
+      max_x = length(hd(grid)) - 1
+      max_y = length(grid) - 1
+
+      trees =
+        for {row, y} <- Enum.with_index(grid), {height, x} <- Enum.with_index(row), into: %{} do
+          {{x, y}, %Tree{height: String.to_integer(height)}}
+        end
+
+      {{max_x, max_y}, trees}
+    else
+      _ -> :error
+    end
+  end
+
+  #######################
+  # HERE BE BOILERPLATE #
+  #######################
+
+  def run do
+    case input() do
+      :error -> print_usage()
+      input -> run_parts_with_timer(input)
+    end
+  end
+
+  defp run_parts_with_timer(input) do
+    run_with_timer(1, fn -> part1(input) end)
+    run_with_timer(2, fn -> part2(input) end)
+  end
+
+  defp run_with_timer(part, fun) do
+    {time, result} = :timer.tc(fun)
+    IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
+    IO.puts("#{result}\n")
+  end
+
+  defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
+  defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
+  defp format_time(μsec), do: "#{μsec / 1_000_000}s"
+
+  defp print_usage do
+    IO.puts("Usage: elixir day8.exs input_filename")
+  end
+end
+
+Day8.run()