[2023-06] Solution (#40)

README.md

@@ -77,7 +77,7 @@ You can read more about `mix test` options
 | 3   | 🌟   |      |      |      |      | 🌟   | 🌟   | 🌟   | 🌟   |
 | 4   | 🌟   |      |      |      |      | 🌟   | 🌟   | 🌟   | 🌟   |
 | 5   | 🌟   |      |      |      |      | 🌟   | 🌟   | 🌟   |      |
-| 6   |      |      |      |      |      | 🌟   | 🌟   | 🌟   |      |
+| 6   |      |      |      |      |      | 🌟   | 🌟   | 🌟   | 🌟   |
 | 7   |      |      |      |      |      | 🌟   | 🌟   | 🌟   |      |
 | 8   |      |      |      |      |      | 🌟   | 🌟   | 🌟   |      |
 | 9   |      |      |      |      |      | 🌟   | 🌟   | 🌟   |      |

lib/advent/y2023/d06.ex

@@ -0,0 +1,69 @@
+defmodule Advent.Y2023.D06 do
+  @moduledoc """
+  https://adventofcode.com/2023/day/6
+  """
+
+  @doc """
+  """
+  @spec part_one(Enumerable.t()) :: any()
+  def part_one(input) do
+    input
+    |> parse_input_01()
+    |> Enum.map(fn {t, d} ->
+      narrow(t, d, 1, t - 1)
+    end)
+    |> Enum.product()
+  end
+
+  @doc """
+  """
+  @spec part_two(Enumerable.t()) :: any()
+  def part_two(input) do
+    [time, distance] = parse_input_02(input)
+    narrow(time, distance, 1, time - 1)
+  end
+
+  defp narrow(time, to_beat, lo, hi) do
+    lo_d = dist(lo, time)
+    hi_d = dist(hi, time)
+
+    if lo_d > to_beat && hi_d > to_beat do
+      Range.size(lo..hi)
+    else
+      lo = if lo_d <= to_beat, do: lo + 1, else: lo
+      hi = if hi_d <= to_beat, do: hi - 1, else: hi
+      narrow(time, to_beat, lo, hi)
+    end
+  end
+
+  defp dist(hold, time) do
+    hold * (time - hold)
+  end
+
+  @spec parse_input_01(Enumerable.t()) :: Enumerable.t()
+  defp parse_input_01(input) do
+    input
+    |> Enum.map(fn line ->
+      line
+      |> String.trim()
+      |> String.split()
+      |> tl()
+      |> Enum.map(&String.to_integer/1)
+    end)
+    |> Enum.zip()
+  end
+
+  @spec parse_input_02(Enumerable.t()) :: Enumerable.t()
+  defp parse_input_02(input) do
+    input
+    |> Enum.map(fn line ->
+      line
+      |> String.trim()
+      |> String.split()
+      |> tl()
+      |> Enum.map(&String.to_integer/1)
+      |> Enum.flat_map(&Integer.digits/1)
+      |> Integer.undigits()
+    end)
+  end
+end

priv/puzzle_input/y2023/d06.txt

@@ -0,0 +1,2 @@
+Time:        40     70     98     79
+Distance:   215   1051   2147   1005

test/advent/y2023/d06_test.exs

@@ -0,0 +1,16 @@
+defmodule Advent.Y2023.D06Test do
+  use TestHelper
+
+  @example_input [
+    "Time:      7  15   30",
+    "Distance:  9  40  200"
+  ]
+
+  aoc_test(
+    example_input: @example_input,
+    p1_example_solution: 288,
+    p1_solution: 1_084_752,
+    p2_example_solution: 71_503,
+    p2_solution: 28_228_952
+  )
+end