day 7

lib/2023/day7.ex

@@ -0,0 +1,113 @@
+defmodule Mix.Tasks.Day7 do
+  use Mix.Task
+  def run(_) do
+    IO.stream() |> solve() |> IO.puts()
+  end
+  @card_ordering_1 [?A, ?K, ?Q, ?J, ?T, ?9,  ?8,  ?7, ?6,  ?5,  ?4,  ?3,  ?2]
+  @card_ordering_2 [?A, ?K, ?Q, ?T, ?9,  ?8,  ?7, ?6,  ?5,  ?4,  ?3,  ?2, ?J]
+  @cards ["A", "K", "Q", "T", "9", "8", "7", "6", "5", "4", "3", "2"]
+
+  def sort_by_hand_ascending(h1, h2, part) do
+    # case Cards.is_stronger_by_hand_type(h1, h2) do
+    #   :win -> false
+    #   :loss -> true
+    #   :draw -> Cards.is_stronger_by_card_type(h2, h1) === :win
+    # end
+    h1t = hand_type(h1, part)
+    h2t = hand_type(h2, part)
+
+    cond do
+      h1t > h2t -> false
+      h1t < h2t -> true
+      h2t === h1t -> compare_hands_by_card_type(h2, h1, part) === :win
+    end
+  end
+
+  defp get_card_index(c, ordering) do
+    Enum.find_index(ordering, &(&1 === c))
+  end
+
+  defp compare_cards(c1, c2, part) do
+    ordering = if part === :part1, do: @card_ordering_1, else: @card_ordering_2 
+    c1_idx = get_card_index(c1, ordering)
+    c2_idx = get_card_index(c2, ordering)
+
+    cond do
+      c1_idx < c2_idx -> :win
+      c2_idx < c1_idx -> :loss
+      true -> :draw
+    end
+  end
+
+  defp compare_hands_by_card_type(<<c1::8>> <> rest1, <<c2::8>> <> rest2, part) do
+    case compare_cards(c1, c2, part) do
+      :draw -> compare_hands_by_card_type(rest1, rest2, part)
+      other -> other
+    end
+  end
+  
+  defp generate_all_hands(h1) do
+    cond do
+      h1 |> String.contains?("J") -> for card <- @cards,
+
+      new_card <- generate_all_hands(h1 |> String.replace("J", card, global: false)) do
+        new_card
+      end
+      true -> [h1]
+    end
+  end
+
+  defp brute_force_best_hand(h1) do
+    cache = Process.get(:key_cache, %{})
+    cond do
+      cache |> Map.has_key?(h1) -> Map.get(cache, h1) |> hand_type(:part2)
+      true -> best = generate_all_hands(h1)
+        |> Enum.sort(fn cand1, cand2 ->
+
+          hand_type(cand1, :part2) > hand_type(cand2, :part2)
+        end)
+        |> Enum.at(0)
+        Process.put(:key_cache, cache |> Map.put(h1, best))
+        best |> hand_type(:part2)
+    end
+  end
+
+  defp hand_type(h1, part) do
+    values = h1 |> String.graphemes() |> Enum.frequencies() |> Map.values()
+    cond do
+      part === :part2 and h1 |> String.contains?("J") -> brute_force_best_hand(h1)
+      # five of kind
+      values |> Enum.any?(&(&1 === 5)) -> 7
+      # four of kind
+      values |> Enum.any?(&(&1 === 4)) -> 6
+      # full house
+      values |> Enum.any?(&(&1 === 3)) &&
+      values |> Enum.any?(&(&1 === 2)) -> 5
+      # three
+      values |> Enum.any?(&(&1 === 3)) -> 4
+      # two pair
+      values |> Enum.filter(&(&1 === 2)) |> Enum.count() === 2 -> 3
+      # one
+      values |> Enum.filter(&(&1 === 2)) |> Enum.count() === 1 -> 2
+      # high card
+      values |> Enum.all?(&(&1 === 1)) -> 1
+    end
+  end
+
+  def solve(input) do
+    part = :part1
+    Process.delete(:key_cache)
+    input
+      |> Enum.map(fn line -> line |> String.trim() |> String.split(" ") |> List.to_tuple() end)
+      |> Enum.sort(fn {h1, _}, {h2, _} -> sort_by_hand_ascending(h1, h2, part) end)
+      |> Enum.with_index()
+      |> Enum.reduce(
+        0,
+        fn {{hand, bid}, i}, acc ->
+          IO.puts(hand)
+          bid = String.to_integer(bid)
+          acc + bid * (i+1)
+        end
+      )
+  end
+end