2023 day 3, part 1

README.md

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 My Elixir solutions for [Advent of Code](https://adventofcode.com/) (all years).
 
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lib/y2023/README.md

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 My Elixir solutions for [Advent of Code 2023](https://adventofcode.com/2023).
 
-<!-- stars 2023 start --><img src="https://img.shields.io/static/v1?label=2023&message=4%20stars&style=for-the-badge&color=red" alt="4 stars" /><!-- stars 2023 end -->
+<!-- stars 2023 start --><img src="https://img.shields.io/static/v1?label=2023&message=5%20stars&style=for-the-badge&color=red" alt="5 stars" /><!-- stars 2023 end -->
 
 ## Benchmarks
 

lib/y2023/day03.ex

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+defmodule Y2023.Day03 do
+  use Advent.Day, no: 03
+
+  def part1(%{numbers: numbers, symbols: symbols}) do
+    symbol_positions = Map.keys(symbols)
+
+    numbers
+    |> Enum.filter(&next_to_symbol?(&1, symbol_positions))
+    |> Enum.map(fn {_, %{number: number}} -> number end)
+    |> Enum.sum()
+  end
+
+  defp next_to_symbol?({position, %{length: length}}, symbol_positions) do
+    position
+    |> calculate_surrounding_positions(length)
+    |> Enum.any?(&Enum.member?(symbol_positions, &1))
+  end
+
+  defp calculate_surrounding_positions({row, col}, length) do
+    [{row, col - 1}, {row, col + length}] ++
+      row_positions(row + 1, col, length) ++ row_positions(row - 1, col, length)
+  end
+
+  defp row_positions(row, col, length) do
+    Enum.map((col - 1)..(col + length), &{row, &1})
+  end
+
+  # @doc """
+  # iex> Day03.part2("update or delete me")
+  # "update or delete me"
+  # """
+  # def part2(input) do
+  #   input
+  # end
+
+  def parse_input(input) do
+    input
+    |> String.split("\n", trim: true)
+    |> Enum.with_index()
+    |> Enum.reduce(%{numbers: %{}, symbols: %{}}, fn {row, row_no}, acc ->
+      %{
+        numbers: read_numbers(row, row_no, acc.numbers),
+        symbols: read_symbols(row, row_no, acc.symbols)
+      }
+    end)
+  end
+
+  # Store a map of all of the numbers in the input, in the format
+  # `%{{row, col} => %{number: number, length: length}`
+  defp read_numbers(row, row_no, acc) do
+    numbers = Regex.scan(~r/[0-9]+/, row, return: :binary)
+    indexes = Regex.scan(~r/[0-9]+/, row, return: :index)
+
+    numbers
+    |> Enum.zip(indexes)
+    |> Enum.reduce(acc, fn {[number], [{col, length}]}, acc ->
+      Map.put(acc, {row_no, col}, %{number: String.to_integer(number), length: length})
+    end)
+  end
+
+  # Store a map of all of the symbols in the input, in the format
+  # `%{{row, col} => "symbol"}`
+  defp read_symbols(row, row_no, acc) do
+    row
+    |> String.graphemes()
+    |> Enum.with_index()
+    |> Enum.reduce(acc, fn {val, col_no}, acc ->
+      if val not in [".", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"] do
+        Map.put(acc, {row_no, col_no}, val)
+      else
+        acc
+      end
+    end)
+  end
+
+  def part1_verify, do: input() |> parse_input() |> part1()
+  # def part2_verify, do: input() |> parse_input() |> part2()
+end