fix: test are passing for part 2

lib/advent_code2024/solutions/day04/day4.ex

@@ -62,7 +62,7 @@ defmodule AdventCode2024.Solutions.Day04 do
   end
 
   defp within_bounds?(grid, row, col) do
-    row >= 0 && row < length(grid) && col >= 0 && col < length(Enum.at(grid, 0))
+    row >= 0 and row < length(grid) and col >= 0 and col < length(Enum.at(grid, 0))
   end
 
   @doc """
@@ -85,68 +85,76 @@ defmodule AdventCode2024.Solutions.Day04 do
   def solve_part2(_input_file) do
   end
 
-  def count_x_mas(grid) when is_list(grid) do
-    # Convert string rows to character grid
-    char_grid = Enum.map(grid, &String.graphemes/1)
-    rows = length(char_grid)
-    cols = length(Enum.at(char_grid, 0))
+  def count_x_mas(grid) do
+    processed_grid = Enum.map(grid, &String.graphemes/1)
 
-    # Check each possible center position
-    for row <- 1..(rows - 2),
-        col <- 1..(cols - 2),
-        reduce: 0 do
-      acc ->
-        if is_x_mas_pattern?(char_grid, {row, col}) do
-          acc + 1
+    processed_grid
+    |> Enum.with_index()
+    |> Enum.reduce(0, fn {row, row_idx}, acc ->
+      row
+      |> Enum.with_index()
+      |> Enum.reduce(acc, fn {cell, col_idx}, acc_inner ->
+        if cell == "A" do  # Start from the center A
+          acc_inner + check_x_patterns(processed_grid, {row_idx, col_idx})
         else
-          acc
+          acc_inner
         end
-    end
+      end)
+    end)
   end
 
-  defp is_x_mas_pattern?(grid, {row, col}) do
-    # Get the center character first
-    center = get_char(grid, row, col)
-    if center != "A", do: false,
-    else: check_diagonals(grid, row, col)
-  end
-
-  defp check_diagonals(grid, row, col) do
-    # Define the four diagonal directions from center
-    diagonals = [
-      [{-1, -1}, {1, 1}],  # top-left to bottom-right
-      [{-1, 1}, {1, -1}],  # top-right to bottom-left
-    ]
-
-    # For each diagonal pair, check if either forms a valid MAS pattern
-    Enum.any?(diagonals, fn [d1, d2] ->
-      chars1 = get_diagonal_chars(grid, row, col, d1)
-      chars2 = get_diagonal_chars(grid, row, col, d2)
-      
-      case {chars1, chars2} do
-        {[c1, "A", c3], [c4, "A", c6]} when not is_nil(c1) and not is_nil(c3) and not is_nil(c4) and not is_nil(c6) ->
-          (is_mas?(c1, c3) and is_mas?(c4, c6)) or
-          (is_mas?(c3, c1) and is_mas?(c6, c4))
-        _ -> false
+  defp check_x_patterns(grid, {row, col}) do
+    # Check both 1-step and 2-step patterns
+    [1, 2]
+    |> Enum.reduce(0, fn step, acc ->
+      if check_x_pattern(grid, {row, col}, step) do
+        acc + 1
+      else
+        acc
       end
     end)
   end
 
-  defp get_diagonal_chars(grid, row, col, {dr, dc}) do
-    [
-      get_char(grid, row - dr, col - dc),
-      get_char(grid, row, col),
-      get_char(grid, row + dr, col + dc)
-    ]
+  defp check_x_pattern(grid, {row, col}, step) do
+    # Check if we can form an X pattern with MAS on both diagonals
+    check_diagonal(grid, {row, col}, {-step, -step}, {step, step}) and  # top-left to bottom-right
+    check_diagonal(grid, {row, col}, {-step, step}, {step, -step})      # top-right to bottom-left
   end
 
-  defp get_char(grid, row, col) do
-    if within_bounds?(grid, row, col) do
-      Enum.at(Enum.at(grid, row), col)
-    end
+  defp check_diagonal(grid, {center_row, center_col}, {top_dr, top_dc}, {bottom_dr, bottom_dc}) do
+    # Check top part and bottom part
+    top_row = center_row + top_dr
+    top_col = center_col + top_dc
+    bottom_row = center_row + bottom_dr
+    bottom_col = center_col + bottom_dc
+
+    within_bounds?(grid, top_row, top_col) and
+    within_bounds?(grid, bottom_row, bottom_col) and
+    (
+      # Check normal orientation (M at top, S at bottom)
+      (Enum.at(Enum.at(grid, top_row), top_col) == "M" and
+       Enum.at(Enum.at(grid, bottom_row), bottom_col) == "S") or
+      # Check upside down orientation (S at top, M at bottom)
+      (Enum.at(Enum.at(grid, top_row), top_col) == "S" and
+       Enum.at(Enum.at(grid, bottom_row), bottom_col) == "M")
+    )
   end
 
-  defp is_mas?(first, last) do
-    first == "M" and last == "S"
+  @doc """
+  Reads a grid from a file and counts the occurrences of a word using `count_word/2`.
+
+  ## Parameters
+  - file_path: The path to the file containing the grid.
+  - word: The word to be searched for.
+
+  ## Returns
+  - The number of times the word is found in the grid.
+  """
+  def count_word_from_file(file_path, word) do
+    file_path
+    |> File.stream!()
+    |> Enum.map(&String.trim/1)
+    |> Enum.map(&String.graphemes/1)
+    |> count_word_occurrences(word)
   end
 end