Day 8

lib/day8/day8.ex

@@ -0,0 +1,71 @@
+defmodule Day8 do
+  def part1 do
+    File.read!("lib/day8/input.txt")
+    |> parse_input()
+    |> split_into_layers(25, 6)
+    |> min_zeros()
+    |> ones_times_twos()
+
+    # "123456789012"
+    # |> parse_input()
+    # |> split_into_layers(3, 2)
+    # |> min_zeros()
+    # |> ones_times_twos()
+  end
+
+  def part2 do
+    File.read!("lib/day8/input.txt")
+    |> parse_input()
+    |> split_into_layers(25, 6)
+    |> combine_layers()
+    |> Enum.map(fn
+      0 -> ?\s
+      1 -> ?X
+    end)
+    |> Enum.chunk_every(25)
+    |> Enum.each(&IO.puts/1)
+
+    # "0222112222120000"
+    # |> parse_input()
+    # |> split_into_layers(2, 2)
+    # |> combine_layers()
+  end
+
+  def parse_input(str) do
+    str
+    |> String.trim()
+    |> String.to_charlist()
+    |> Enum.map(fn digit -> digit - ?0 end)
+  end
+
+  def split_into_layers(input, layer_width, layer_height) do
+    Enum.chunk_every(input, layer_width * layer_height)
+  end
+
+  def min_zeros(layers) do
+    layers
+    |> Enum.min_by(fn layer ->
+      Enum.count(layer, &(&1 == 0))
+    end)
+  end
+
+  def ones_times_twos(layer) do
+    ones = Enum.count(layer, &(&1 == 1))
+    twos = Enum.count(layer, &(&1 == 2))
+    ones * twos
+  end
+
+  def combine_layers(layers) do
+    Enum.zip(layers)
+    |> Enum.map(&combine_pixel/1)
+  end
+
+  def combine_pixel(pixel) do
+    0..(tuple_size(pixel) - 1)
+    |> Enum.map(fn index -> elem(pixel, index) end)
+    |> Enum.reduce(2, fn
+      val, 2 -> val
+      _, it -> it
+    end)
+  end
+end