Solve 2021 Day 3 Part 1 in elixir

2021/Day3/Elixir/binary_diagnostics.ex

@@ -0,0 +1,48 @@
+# iex()> Day3.first
+
+defmodule BinaryDiagnostics do
+  def load_file() do
+    File.read!("../input.txt")
+    |> String.split("\n", trim: true)
+  end
+
+  def most_common(list) do
+    gb = Enum.group_by(list, & &1)
+    max = Enum.map(gb, fn {_, val} -> length(val) end) |> Enum.max()
+    [most_common] = for {key, val} <- gb, length(val) == max, do: key
+    most_common
+  end
+
+  def least_common(list) do
+    gb = Enum.group_by(list, & &1)
+    min = Enum.map(gb, fn {_, val} -> length(val) end) |> Enum.min()
+    [least_common] = for {key, val} <- gb, length(val) == min, do: key
+    least_common
+  end
+
+  def get_result(binary_list, comparator) do
+    binary_list
+    |> Enum.map(fn bin -> String.split(bin, "", trim: true) end)
+    |> Enum.zip_reduce([], fn elements, acc ->
+      [comparator.(elements) | acc]
+    end)
+    |> Enum.reverse()
+    |> Enum.join("")
+    |> Integer.parse(2)
+    |> elem(0)
+  end
+
+  @spec first() :: Integer
+  def first() do
+    binaries = load_file
+    gamma = get_result(binaries, &most_common/1)
+    epsilon = get_result(binaries, &least_common/1)
+
+    gamma * epsilon
+  end
+
+  @spec second() :: Integer
+  def second() do
+    :second
+  end
+end