Day 19 part 1

1 files changed, 37 insertions, 0 deletions

diff --git a/2015/day19.exs b/2015/day19.exs
new file mode 100644
index 0000000..2aae946
--- /dev/null
+++ b/2015/day19.exs
@@ -0,0 +1,37 @@
+{replacements, medicine} =
+  File.stream!("inputs/day19.txt")
+  |> Stream.map(&String.trim/1)
+  |> Stream.filter(&(&1 != ""))
+  |> Stream.map(fn line ->
+    case Regex.run(~r/(\w+) => (\w+)/, line) do
+      [_, from, to] -> {:replacement, from, to}
+      _ -> {:start, line}
+    end
+  end)
+  |> Enum.reduce({[], nil}, fn
+    {:replacement, from, to}, {replacements, start} -> {[{from, to} | replacements], start}
+    {:start, start}, {replacements, _start} -> {replacements, start}
+  end)
+
+nextGen = fn start ->
+  Enum.flat_map(0..(String.length(start) - 1), fn offset ->
+    {beforeReplace, replaceStart} = String.split_at(start, offset)
+
+    Enum.filter(replacements, fn {from, _} -> String.starts_with?(replaceStart, from) end)
+    |> Enum.map(fn {from, to} ->
+      {^from, afterReplace} = String.split_at(replaceStart, String.length(from))
+      <<beforeReplace <> to <> afterReplace>>
+    end)
+  end)
+  |> Enum.uniq()
+end
+
+calibration = nextGen.(medicine)
+
+IO.puts("Calibration size: #{length(calibration)}")
+
+medicineGeneration =
+  Stream.iterate(["e"], fn gen -> Enum.flat_map(gen, &nextGen.(&1)) |> Enum.uniq() end)
+  |> Enum.find_index(fn gen -> Enum.any?(gen, &(&1 == medicine)) end)
+
+IO.puts("The Medicine generation: #{medicineGeneration}")