⚡ Add solution to Day 7 part 2

advent_of_code/lib/advent_of_code.ex

@@ -27,5 +27,6 @@ defmodule AdventOfCode do
     print(6, 1, Day6.part1())
     print(6, 2, Day6.part2())
     print(7, 1, Day7.part1())
+    print(7, 2, Day7.part2())
   end
 end

advent_of_code/lib/day_7.ex

@@ -1,24 +1,34 @@
 defmodule Day7 do
-  def classify_hand({hand, bid}) do
+  def classify_hand({hand, bid}, jokers \\ false) do
     hand =
       hand
       |> String.to_charlist()
       |> Enum.map(
         &case &1 do
           ?T -> "A"
-          ?J -> "B"
+          ?J -> if jokers, do: "1", else: "B"
           ?Q -> "C"
           ?K -> "D"
           ?A -> "E"
           x -> x
         end
       )
 
+    {jokers, non_jokers} = hand |> Enum.split_with(&(&1 == "1"))
+    jokers = jokers |> Enum.count()
+
     type =
-      hand
+      non_jokers
       |> Enum.frequencies()
       |> Map.values()
       |> Enum.sort(:desc)
+      |> Kernel.then(fn list ->
+        if list == [] do
+          [5]
+        else
+          [hd(list) + jokers | tl(list)]
+        end
+      end)
       |> case do
         [5] -> 7
         [4, 1] -> 6
@@ -38,13 +48,21 @@ defmodule Day7 do
     |> Stream.map(fn [hand, bid] -> {hand, String.to_integer(bid)} end)
   end
 
-  def part1(stream \\ Inputs.stream(7)) do
+  def solve(stream, jokers \\ false) do
     stream
     |> parse_hands()
-    |> Stream.map(&classify_hand/1)
+    |> Stream.map(&classify_hand(&1, jokers))
     |> Enum.sort()
     |> Enum.with_index(1)
     |> Enum.map(fn {{_, _, bid}, rank} -> bid * rank end)
     |> Enum.sum()
   end
+
+  def part1(stream \\ Inputs.stream(7)) do
+    stream |> solve()
+  end
+
+  def part2(stream \\ Inputs.stream(7)) do
+    stream |> solve(true)
+  end
 end

advent_of_code/test/day7_test.exs

@@ -24,12 +24,18 @@ defmodule Day7Test do
              ] == hands
     end
 
-    test "Day7.classify_hand/1" do
+    test "Day7.classify_hand/2" do
       assert {2, "32A3D", 765} = Day7.classify_hand({"32T3K", 765})
       assert {4, "A55B5", 684} = Day7.classify_hand({"T55J5", 684})
       assert {3, "DD677", 28} = Day7.classify_hand({"KK677", 28})
       assert {3, "DABBA", 220} = Day7.classify_hand({"KTJJT", 220})
       assert {4, "CCCBE", 483} = Day7.classify_hand({"QQQJA", 483})
+
+      assert {2, "32A3D", 765} = Day7.classify_hand({"32T3K", 765}, true)
+      assert {6, "A5515", 684} = Day7.classify_hand({"T55J5", 684}, true)
+      assert {3, "DD677", 28} = Day7.classify_hand({"KK677", 28}, true)
+      assert {6, "DA11A", 220} = Day7.classify_hand({"KTJJT", 220}, true)
+      assert {6, "CCC1E", 483} = Day7.classify_hand({"QQQJA", 483}, true)
     end
 
     test "sorting" do
@@ -46,10 +52,28 @@ defmodule Day7Test do
                {3, "DABBA", 220},
                {2, "32A3D", 765}
              ] == hands
+
+      hands =
+        @example_input
+        |> Day7.parse_hands()
+        |> Stream.map(&Day7.classify_hand(&1, true))
+        |> Enum.sort(:desc)
+
+      assert [
+               {6, "DA11A", 220},
+               {6, "CCC1E", 483},
+               {6, "A5515", 684},
+               {3, "DD677", 28},
+               {2, "32A3D", 765}
+             ] == hands
     end
 
     test "Day7.part1/1" do
       assert 6440 == Day7.part1(@example_input)
     end
+
+    test "Day7.part2/1" do
+      assert 5905 == Day7.part2(@example_input)
+    end
   end
 end