Solve 2016/11

Author: code-shoily

lib/2016/day_11.ex

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+defmodule AdventOfCode.Y2016.Day11 do
+  @moduledoc """
+  --- Day 11: Radioisotope Thermoelectric Generators ---
+  Problem Link: https://adventofcode.com/2016/day/11
+  Difficulty: l
+  Tags: simulation graph state-space manual-parse
+  """
+  alias Yog.Traversal.Implicit
+
+  def run(_input \\ "") do
+    # Manual parse based on 2016_11.txt
+    # Floor 1: strontium(S) G,M, plutonium(P) G,M
+    # Floor 2: thulium(T) G, ruthenium(R) G,M, curium(C) G,M
+    # Floor 3: thulium(T) M
+    # Floor 4: -
+    # State: {elevator_floor, sorted_pairs} where pair = {m_floor, g_floor}
+    p1_initial = {1, sort_pairs([{1, 1}, {1, 1}, {3, 2}, {2, 2}, {2, 2}])}
+
+    # Part 2: add Elerium and Dilithium pairs on floor 1
+    p2_initial = {1, sort_pairs([{1, 1}, {1, 1} | elem(p1_initial, 1)])}
+
+    {solve(p1_initial), solve(p2_initial)}
+  end
+
+  defp solve(initial_state) do
+    Implicit.implicit_fold(
+      from: initial_state,
+      using: :breadth_first,
+      initial: nil,
+      successors_of: fn state -> generate_successors(state) end,
+      with: fn
+        _acc, {4, pairs}, meta ->
+          if Enum.all?(pairs, fn {m, g} -> m == 4 and g == 4 end) do
+            {:halt, meta.depth}
+          else
+            {:continue, nil}
+          end
+
+        _acc, _state, _meta ->
+          {:continue, nil}
+      end
+    )
+  end
+
+  defp generate_successors({floor, pairs}) do
+    # Pruning: Don't go back down to empty floors
+    lowest_occupied =
+      Enum.find(1..4, fn f ->
+        Enum.any?(pairs, fn {m, g} -> m == f or g == f end)
+      end) || 4
+
+    next_floors = for f <- [floor - 1, floor + 1], f in 1..4, f >= lowest_occupied, do: f
+
+    items =
+      for {pair, idx} <- Enum.with_index(pairs),
+          type <- [:m, :g],
+          item_floor(pair, type) == floor,
+          do: {idx, type}
+
+    one_item = for item <- items, do: [item]
+    two_items = for i1 <- items, i2 <- items, i1 < i2, do: [i1, i2]
+
+    for nf <- next_floors,
+        load <- one_item ++ two_items,
+        new_pairs = move(pairs, nf, load),
+        valid?(new_pairs),
+        do: {nf, sort_pairs(new_pairs)}
+  end
+
+  defp item_floor({m, _g}, :m), do: m
+  defp item_floor({_m, g}, :g), do: g
+
+  defp move(pairs, next_floor, items_to_move) do
+    Enum.reduce(items_to_move, pairs, fn {idx, type}, acc ->
+      List.update_at(acc, idx, fn {m, g} ->
+        if type == :m, do: {next_floor, g}, else: {m, next_floor}
+      end)
+    end)
+  end
+
+  defp sort_pairs(pairs), do: Enum.sort(pairs)
+
+  defp valid?(pairs) do
+    Enum.all?(1..4, fn floor ->
+      has_generator = Enum.any?(pairs, fn {_m, g} -> g == floor end)
+
+      if has_generator do
+        Enum.all?(pairs, fn {m, g} ->
+          if m == floor, do: g == floor, else: true
+        end)
+      else
+        true
+      end
+    end)
+  end
+end

priv/input_files/2016_11.txt

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+The first floor contains a strontium generator, a strontium-compatible microchip, a plutonium generator, and a plutonium-compatible microchip.
+The second floor contains a thulium generator, a ruthenium generator, a ruthenium-compatible microchip, a curium generator, and a curium-compatible microchip.
+The third floor contains a thulium-compatible microchip.
+The fourth floor contains nothing relevant.

test/2016/day_11_test.exs

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+defmodule AdventOfCode.Y2016.Day11Test do
+  @moduledoc false
+
+  use ExUnit.Case, async: true
+  @moduletag :y1611
+
+  alias AdventOfCode.Y2016.Day11, as: Solution
+
+  test "Year 2016, Day 11 run/1" do
+    assert Solution.run() == {37, 61}
+  end
+end

wiki/tags/manual-parse.md

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+# Tag: `manual-parse`
+
+[← Tags Index](index.md)  |  [← Home](../../README.md)
+
+| Year | Day | Title | Difficulty | Other Tags | Source |
+|------|:---:|-------|:----------:|------------|--------|
+| 2016 | [11](https://adventofcode.com/2016/day/11) | [Radioisotope Thermoelectric Generators](https://adventofcode.com/2016/day/11) | 🔴 | [simulation](simulation.md), [graph](graph.md), [state-space](state-space.md) | [day_11.ex](../../lib/2016/day_11.ex) |