Finished day 5

day5.livemd

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+# AOC 2022 - Day 5
+
+```elixir
+Mix.install([
+  {:req, "~> 0.3.3"},
+  {:nimble_parsec, "~> 1.2.3"}
+])
+```
+
+## Puzzle description
+
+[Day 5: Supply Stacks](https://adventofcode.com/2022/day/5).
+
+## Input
+
+```elixir
+defmodule Load do
+  def input do
+    aoc_session = System.fetch_env!("LB_AOC_SESSION")
+    input_url = "https://adventofcode.com/2022/day/5/input"
+    Req.get!(input_url, headers: [cookie: "session=#{aoc_session}"]).body
+  end
+end
+```
+
+## Solution
+
+```elixir
+defmodule Parser do
+  import NimbleParsec
+
+  crate =
+    ignore(string("["))
+    |> utf8_char([?A..?Z])
+    |> ignore(string("]"))
+
+  empty_slot = string("   ") |> replace(:empty)
+
+  slot = choice([crate, empty_slot])
+
+  row =
+    repeat_while(
+      concat(
+        slot,
+        optional(ignore(string(" ")))
+      ),
+      :not_newline
+    )
+    |> ignore(string("\n"))
+    |> tag(:row)
+
+  rows =
+    repeat_while(row, :not_index_row)
+    |> tag(:rows)
+
+  indices =
+    repeat_while(
+      ignore(string(" "))
+      |> integer(min: 1)
+      |> ignore(string(" "))
+      |> optional(ignore(string(" "))),
+      :not_newline
+    )
+    |> ignore(string("\n"))
+    |> tag(:indices)
+
+  instruction =
+    ignore(string("move "))
+    |> unwrap_and_tag(integer(min: 1), :amount)
+    |> ignore(string(" from "))
+    |> unwrap_and_tag(integer(min: 1), :from)
+    |> ignore(string(" to "))
+    |> unwrap_and_tag(integer(min: 1), :to)
+    |> ignore(optional(string("\n")))
+    |> tag(:instruction)
+
+  instructions = instruction |> repeat() |> tag(:instructions) |> eos()
+
+  defparsec(
+    :crates,
+    rows
+    |> concat(indices)
+    |> concat(ignore(string("\n")))
+    |> concat(instructions)
+  )
+
+  defp not_newline(<<?\n, _::binary>>, context, _, _), do: {:halt, context}
+  defp not_newline(_, context, _, _), do: {:cont, context}
+
+  defp not_index_row(<<" 1", _::binary>>, context, _, _), do: {:halt, context}
+  defp not_index_row(_, context, _, _), do: {:cont, context}
+end
+
+# Parser.rows(~s([S]     [C]
+# [P] [M] [Z]
+#  1   2   3)) |> IO.inspect()
+
+# Parser.slot("   ") |> IO.inspect()
+# Parser.slot("brt") |> IO.inspect()
+```
+
+```elixir
+
+```
+
+```elixir
+defmodule Part1 do
+  def run(input) do
+    {:ok, data, _, _, _, _} =
+      input
+      |> Parser.crates()
+
+    stacks =
+      data
+      |> Keyword.get(:rows)
+      |> Keyword.values()
+      |> List.zip()
+      |> Enum.map(&Tuple.to_list/1)
+      |> Enum.map(
+        &Enum.reject(&1, fn
+          :empty -> true
+          _ -> false
+        end)
+      )
+
+    instructions =
+      data
+      |> Keyword.get(:instructions)
+      |> Keyword.values()
+
+    instructions
+    |> Enum.reduce(stacks, fn [amount: amount, from: from, to: to], acc ->
+      from = from - 1
+      to = to - 1
+
+      {transfer, from_stack} =
+        Enum.at(acc, from)
+        |> Enum.split(amount)
+
+      to_stack =
+        transfer
+        |> Enum.reverse()
+        |> Enum.concat(Enum.at(acc, to))
+
+      List.replace_at(acc, from, from_stack)
+      |> List.replace_at(to, to_stack)
+    end)
+    |> Enum.map(&Enum.take(&1, 1))
+    |> Enum.join()
+  end
+end
+
+defmodule Part2 do
+  def run(input) do
+    {:ok, data, _, _, _, _} =
+      input
+      |> Parser.crates()
+
+    stacks =
+      data
+      |> Keyword.get(:rows)
+      |> Keyword.values()
+      |> List.zip()
+      |> Enum.map(&Tuple.to_list/1)
+      |> Enum.map(
+        &Enum.reject(&1, fn
+          :empty -> true
+          _ -> false
+        end)
+      )
+
+    instructions =
+      data
+      |> Keyword.get(:instructions)
+      |> Keyword.values()
+
+    instructions
+    |> Enum.reduce(stacks, fn [amount: amount, from: from, to: to], acc ->
+      from = from - 1
+      to = to - 1
+
+      {transfer, from_stack} =
+        Enum.at(acc, from)
+        |> Enum.split(amount)
+
+      to_stack =
+        transfer
+        |> Enum.concat(Enum.at(acc, to))
+
+      List.replace_at(acc, from, from_stack)
+      |> List.replace_at(to, to_stack)
+    end)
+    |> Enum.map(&Enum.take(&1, 1))
+    |> Enum.join()
+  end
+end
+
+ExUnit.start(autorun: false)
+
+defmodule Test do
+  use ExUnit.Case, async: true
+  @example_input ~s(    [D]    
+[N] [C]    
+[Z] [M] [P]
+ 1   2   3 
+
+move 1 from 2 to 1
+move 3 from 1 to 3
+move 2 from 2 to 1
+move 1 from 1 to 2)
+  @input Load.input()
+
+  test "it loads the input" do
+    assert String.length(@input) > 0
+  end
+
+  test "part 1 example" do
+    assert Part1.run(@example_input) === "CMZ"
+  end
+
+  test "part 1" do
+    assert Part1.run(@input) === "GFTNRBZPF"
+  end
+
+  test "part 2 example" do
+    assert Part2.run(@example_input) === "MCD"
+  end
+
+  test "part 2" do
+    assert Part2.run(@input) === "VRQWPDSGP"
+  end
+end
+
+ExUnit.run()
+```