[TASK] Day 2, part 1 in Elixir

README.md

@@ -1,3 +1,3 @@
 # advent-of-code-2025
 
-My solutions to advent of code 2025
+My solutions to advent of code 2025. This year I decided to do a different language each day.

day2-elixir/.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

day2-elixir/.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+day2-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/

day2-elixir/input/day2.txt

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+749639-858415,65630137-65704528,10662-29791,1-17,9897536-10087630,1239-2285,1380136-1595466,8238934-8372812,211440-256482,623-1205,102561-122442,91871983-91968838,62364163-62554867,3737324037-3737408513,9494926669-9494965937,9939271919-9939349036,83764103-83929201,24784655-24849904,166-605,991665-1015125,262373-399735,557161-618450,937905586-937994967,71647091-71771804,8882706-9059390,2546-10476,4955694516-4955781763,47437-99032,645402-707561,27-86,97-157,894084-989884,421072-462151

day2-elixir/input/day2_example.txt

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+11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124

day2-elixir/lib/day2.ex

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+defmodule Day2 do
+  @moduledoc """
+  Documentation for `Day2`.
+  """
+  require Integer
+
+  def start(_type, _args) do
+
+    input_file = File.read("input/day2.txt")
+    IO.puts "Part 1: #{Day2.part1(elem(input_file, 1))}"
+  end
+
+  def part1(input) do
+    for range <- String.split(input, ",") do
+      [from, to] = String.split(range, "-") |> Enum.map(fn s -> String.to_integer(s) end)
+      eval_range(from, to)
+    end |> Enum.sum
+  end
+
+  def eval_range(from, to) do
+    Enum.filter(from..to, fn x -> is_valid_id(x) end) |> Enum.sum
+  end
+
+  def is_valid_id(id) do
+    digit_count = Enum.count(Integer.digits(id))
+    power = 10 ** (div(digit_count, 2))
+    # IO.inspect {id, digit_count, power, div(id, power), rem(id, power)}
+    Integer.is_even(digit_count) && div(id, power) == rem(id, power)
+  end
+end

day2-elixir/mix.exs

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+defmodule Day2.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :day2,
+      version: "0.1.0",
+      elixir: "~> 1.18",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      mod: { Day2, []},
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

day2-elixir/test/day2_test.exs

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+defmodule Day2Test do
+  use ExUnit.Case
+  doctest Day2
+
+  test "Part 1 example input" do
+    input_file = File.read("input/day2_example.txt")
+    assert Day2.part1(elem(input_file, 1)) == 1227775554
+  end
+end

day2-elixir/test/test_helper.exs

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+ExUnit.start()