aoc 2024 day 4

elixir/livebook/2024/day4.livemd

@@ -0,0 +1,83 @@
+# AOC 2024 Day 4
+
+## Section
+
+```elixir
+input =  """
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX
+"""
+```
+
+```elixir
+lines = input |> String.trim() |> String.split("\n")
+```
+
+```elixir
+g = Grid2D.new(
+  lines |> Enum.at(0) |> String.trim() |> String.graphemes() |> Enum.count(), 
+  lines |> Enum.count
+)
+```
+
+```elixir
+input = input |> String.replace("\n", "")
+```
+
+```elixir
+find_word = fn 
+  _, w, pl, w, _, _ -> pl
+  input, word, [pos | _] = poslist, curr, dir, f -> 
+    
+    ["", <<next_letter::binary-size(1)>> <> _] = String.split(word, curr)
+    coord = Grid2D.index_to_coord(g, pos)
+    next = Grid2D.add(coord, dir)
+    
+    if Grid2D.in_grid?(next, g) and (next_letter == String.at(input, index)) do
+      index = Grid2D.coord_to_index(g, next)
+      f.(input, word, index, [index | poslist], curr <> next_letter, dir, f)
+    else
+      nil
+    end
+end
+```
+
+```elixir
+for [{idx, _}] <- Regex.scan(~r/X/, input, return: :index),
+    i <- -1..1//1,
+    j <- -1..1//1,
+    j != 0 or i != 0 do
+  find_word.(input, "XMAS", [idx], "X", {i, j}, find_word)
+end |> Enum.reject(&(&1 == nil)) |> Enum.count()
+```
+
+```elixir
+is_xmas? = 
+  fn grid, coord->
+    corners = [{1,1}, {1,-1}, {-1, -1}, {-1, 1}] |> Enum.map(&Grid2D.add(coord, &1))
+    has_corners? = Enum.all?(
+      corners,
+      fn p -> Grid2D.in_grid?(p, g) end
+    ) 
+    corner_letters = (corners |> Enum.map(fn c -> String.at(grid, Grid2D.coord_to_index(g, c)) end))
+    is_mas? = fn -> corner_letters |> Enum.chunk_every(2, 1, :discard) |> Enum.any?(fn i -> i == ["S", "S"] or i == ["M", "M"] end) end
+    has_m? = fn -> (corner_letters |> Enum.count(&(&1 == "M"))) == 2 end
+    has_s? = fn -> (corner_letters |> Enum.count(&(&1 == "S"))) == 2 end
+    has_corners? and has_m?.() and has_s?.() and is_mas?.()
+  end
+```
+
+```elixir
+for [{i, _}] <- Regex.scan(~r/A/, input, return: :index),
+  coord = Grid2D.index_to_coord(g, i) do
+  { coord, is_xmas?.(input, coord)}
+end |> Enum.count(fn {_, t} -> t end)
+```