feat: implement solution to the example

lib/advent_code2024/solutions/day04/day4.ex

@@ -0,0 +1,77 @@
+defmodule AdventCode2024.Solutions.Day04 do
+  def count_word_occurrences(grid, word) do
+    grid
+    |> Enum.map(&String.graphemes/1)
+    |> find_word(word)
+  end
+
+  defp find_word(grid, word) do
+    directions = [
+      # Right
+      {0, 1},
+      # Down
+      {1, 0},
+      # Left
+      {0, -1},
+      # Up
+      {-1, 0},
+      # Down-right diagonal
+      {1, 1},
+      # Up-left diagonal
+      {-1, -1},
+      # Down-left diagonal
+      {1, -1},
+      # Up-right diagonal
+      {-1, 1}
+    ]
+
+    grid
+    |> Enum.with_index()
+    |> Enum.reduce(0, fn {row, row_idx}, acc ->
+      row
+      |> Enum.with_index()
+      |> Enum.reduce(acc, fn {_, col_idx}, acc_inner ->
+        acc_inner + count_word_from(grid, word, {row_idx, col_idx}, directions)
+      end)
+    end)
+  end
+
+  @doc """
+  Counts the occurrences of a word in all possible directions from a given starting position in the grid.
+
+  ## Parameters
+  - grid: A 2D list representing the word search grid.
+  - word: The word to be searched for.
+  - row: The starting row index.
+  - col: The starting column index.
+  - directions: A list of tuples representing the directions to search in.
+
+  ## Returns
+  - The number of times the word is found from the given starting position in the grid.
+  """
+  defp count_word_from(grid, word, {row, col}, directions) do
+    directions
+    |> Enum.reduce(0, fn direction, acc ->
+      if find_word?(grid, word, {row, col}, direction) do
+        acc + 1
+      else
+        acc
+      end
+    end)
+  end
+
+  defp find_word?(grid, word, {row, col}, {d_row, d_col}) do
+    word
+    |> String.codepoints()
+    |> Enum.with_index()
+    |> Enum.all?(fn {char, i} ->
+      new_row = row + i * d_row
+      new_col = col + i * d_col
+      within_bounds?(grid, new_row, new_col) && Enum.at(Enum.at(grid, new_row), new_col) == char
+    end)
+  end
+
+  defp within_bounds?(grid, row, col) do
+    row >= 0 && row < length(grid) && col >= 0 && col < length(Enum.at(grid, 0))
+  end
+end