Move alternative Day5 impl to separate files

day5/README

@@ -45,10 +45,16 @@ I quite enjoyed this one, maybe because it's a Saturday and I wasn't burnt out f
 
 ** Update **
 
-After reading the Elixir Forum thread: https://elixirforum.com/t/advent-of-code-2020-day-5/35997/
+After reading the Elixir Forum thread (https://elixirforum.com/t/advent-of-code-2020-day-5/35997/),
+I really had to have a go at just parsing the boarding pass directly into an integer, so I added
+simplified versions as day5part1-bitstring.exs and day5part2-bitstring.exs
 
-I really had to have a go at just parsing the boarding pass directly into an integer. I said I wouldn't
+They use this bitstring-comprehension:
-commit code to my solutions after reading forums, but as long as it's clearly labelled, I think it's fine.
+
+    <<id::10>> = for <<char <- boarding_pass>>, into: <<>>, do: char_to_bit(char)
+
+    def char_to_bit(c) when c in 'FL', do: <<0::1>>
+    def char_to_bit(c) when c in 'BR', do: <<1::1>>
 
 It converts each character to a bit on the fly, and interprets the result as a 10-bit integer. 🦾
 

day5/day5part1-bitstring.exs

@@ -0,0 +1,19 @@
+defmodule Day5Part1 do
+  def run do
+    File.stream!("input")
+    |> Stream.map(&String.trim/1)
+    |> Stream.map(&seat_id/1)
+    |> Enum.max()
+    |> IO.puts()
+  end
+
+  def char_to_bit(c) when c in 'FL', do: <<0::1>>
+  def char_to_bit(c) when c in 'BR', do: <<1::1>>
+
+  def seat_id(boarding_pass) do
+    <<id::10>> = for <<char <- boarding_pass>>, into: <<>>, do: char_to_bit(char)
+    id
+  end
+end
+
+Day5Part1.run()

day5/day5part1.exs

@@ -27,18 +27,6 @@ defmodule Day5Part1 do
 
     row * 8 + col
   end
-
-  # ALTERNATIVE PARSER ADDED AFTER READING OTHER SUBMISSIONS
-  # The boarding pass is actually just a binary number, so we can parse it as such directly.
-  # (The *8 above is eqivalent to the 3-bit shift to the left)
-  def char_to_bit(c) when c in 'FL', do: <<0::1>>
-  def char_to_bit(c) when c in 'BR', do: <<1::1>>
-
-  def seat_id_bitstring(boarding_pass \\ "FBFBBFFRLR") do
-    boarding_pass = String.trim(boarding_pass)
-    <<id::integer-10>> = for <<char <- boarding_pass>>, into: <<>>, do: char_to_bit(char)
-    id
-  end
 end
 
 Day5Part1.run()

day5/day5part2-bitstring.exs

@@ -0,0 +1,27 @@
+defmodule Day5Part2 do
+  def run do
+    File.stream!("input")
+    |> Stream.map(&String.trim/1)
+    |> Stream.map(&seat_id/1)
+    |> Enum.sort()
+    |> find_seat()
+    |> IO.puts()
+  end
+
+  def find_seat([_ | next_seats] = seats) do
+    Stream.zip(seats, next_seats)
+    |> Enum.find(fn {seat, next} -> next - seat > 1 end)
+    |> elem(0)
+    |> Kernel.+(1)
+  end
+
+  def char_to_bit(c) when c in 'FL', do: <<0::1>>
+  def char_to_bit(c) when c in 'BR', do: <<1::1>>
+
+  def seat_id(boarding_pass) do
+    <<id::10>> = for <<char <- boarding_pass>>, into: <<>>, do: char_to_bit(char)
+    id
+  end
+end
+
+Day5Part2.run()

day5/day5part2.exs

@@ -35,18 +35,6 @@ defmodule Day5Part2 do
 
     row * 8 + col
   end
-
-  # ALTERNATIVE PARSER ADDED AFTER READING OTHER SUBMISSIONS
-  # The boarding pass is actually just a binary number, so we can parse it as such directly.
-  # (The *8 above is eqivalent to the 3-bit shift to the left)
-  def char_to_bit(c) when c in 'FL', do: <<0::1>>
-  def char_to_bit(c) when c in 'BR', do: <<1::1>>
-
-  def seat_id_bitstring(boarding_pass \\ "FBFBBFFRLR") do
-    boarding_pass = String.trim(boarding_pass)
-    <<id::integer-10>> = for <<char <- boarding_pass>>, into: <<>>, do: char_to_bit(char)
-    id
-  end
 end
 
 Day5Part2.run()