Solve day 22 in Elixir

bereal · Dec 22, 2020 · 043ebf4 · 043ebf4
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diff --git a/22_elixir/input.txt b/22_elixir/input.txt
@@ -0,0 +1,53 @@
+Player 1:
+2
+31
+14
+45
+33
+18
+29
+36
+44
+47
+38
+6
+9
+5
+48
+17
+50
+41
+4
+21
+42
+23
+25
+28
+3
+
+Player 2:
+26
+16
+27
+12
+49
+32
+19
+46
+37
+15
+10
+30
+11
+24
+1
+40
+7
+8
+43
+34
+20
+35
+22
+39
+13
diff --git a/22_elixir/run.sh b/22_elixir/run.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+elixir ./solve.exs < input.txt
diff --git a/22_elixir/solve.exs b/22_elixir/solve.exs
@@ -0,0 +1,52 @@
+defmodule Game do
+  def play1(a, []), do: {true, a}
+  def play1([], b), do: {false, b}
+
+  def play1([a | as], [b | bs]) do
+    if a > b, do: play1(as ++ [a, b], bs), else: play1(as, bs ++ [b, a])
+  end
+
+  def play2(p1, p2, mem1 \\ MapSet.new(), mem2 \\ MapSet.new())
+  def play2(a, [], _, _), do: {true, a}
+  def play2([], b, _, _), do: {false, b}
+
+  def play2([a | as] = p1, [b | bs] = p2, mem1, mem2) do
+    win = fn p ->
+      {new_as, new_bs} = if p, do: {as ++ [a, b], bs}, else: {as, bs ++ [b, a]}
+      play2(new_as, new_bs, MapSet.put(mem1, p1), MapSet.put(mem2, p2))
+    end
+
+    cond do
+      MapSet.member?(mem1, p1) or MapSet.member?(mem2, p2) ->
+        {true, p1}
+
+      a <= length(as) and b <= length(bs) ->
+        case play2(Enum.take(as, a), Enum.take(bs, b)) do
+          {p, _} -> win.(p)
+        end
+
+      true ->
+        win.(a > b)
+    end
+  end
+
+  def score({_, deck}) do
+    Enum.reverse(deck) |> Enum.with_index(1) |> Enum.map(fn {a, b} -> a * b end) |> Enum.sum()
+  end
+
+  def read_player(buf \\ []) do
+    case IO.read(:stdio, :line) do
+      e when e in [:eof, "\n"] ->
+        buf |> Enum.reverse() |> Enum.drop(1) |> Enum.map(&String.to_integer/1)
+
+      v ->
+        read_player([String.trim(v) | buf])
+    end
+  end
+
+  def read_input(), do: {read_player(), read_player()}
+end
+
+{p1, p2} = Game.read_input()
+Game.play1(p1, p2) |> Game.score() |> IO.inspect()
+Game.play2(p1, p2) |> Game.score() |> IO.inspect()
diff --git a/README.md b/README.md
@@ -53,6 +53,7 @@ I estimated my knowledge of each language by 0 to 4 scale, roughly meaning:
  | 19  | [JavaScript](#day-19-javascript) | 4 | [Monster Messages](https://adventofcode.com/2020/day/19) | [Link](19_js/solve.js) |
  | 20  | [Scala](#day-20-scala)     | 1   | [Jurassic Jigsaw](https://adventofcode.com/2020/day/20)  | [Link](20_scala/solve.scala) |
  | 21  | [Dart](#day-21-dart)       | 2   | [Allergen Assessment](https://adventofcode.com/2020/day/21) | [Link](21_dart/solve.dart) |
+ | 22  | [Elixir](#day-22-elixir)   | 0   | [Crab Combat](https://adventofcode.com/2020/day/22) | [Link](22_elixir/solve.exs) |
 
 ### Day 1: Erlang
 
@@ -461,7 +462,7 @@ _TBD after the second part is complete_
 
 ### Day 21. Dart
 
-_Knowledge_: 3
+_Knowledge_: 2
 
 _Site_: https://dart.dev/
 
@@ -476,3 +477,19 @@ On the other hand, TS is able to use all the JS code, which is _a lot_ of code.
 The puzzle is essentially the same as on the [day 16](#day-16-c), just differently worded, so the solution is identical.
 
 [Solution](21_dart/solve.dart) | [Up](#languages)
+
+
+### Day 22. Elixir
+
+_Knowledge_: 0
+
+_Site_: https://elixir-lang.org/
+
+_Puzzle_: [Crab Combat](https://adventofcode.com/2020/day/22). Lists and recursion
+
+Elixir is Erlang in Ruby's clothes. The puzzle is all about recursive list processing, so
+a functional language is a no-brainer choice. But all the coolest features, like metaprogramming,
+polymorphism, and concurrency remained unexplored. Well, someday... Having to use `fun.()` syntax
+for variable-bound functions feels a bit awkward.
+
+[Solution](22_elixir/solve.exs) | [Up](#languages)
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,53 @@
		Player 1:
		2
		31
		14
		45
		33
		18
		29
		36
		44
		47
		38
		6
		9
		5
		48
		17
		50
		41
		4
		21
		42
		23
		25
		28
		3

		Player 2:
		26
		16
		27
		12
		49
		32
		19
		46
		37
		15
		10
		30
		11
		24
		1
		40
		7
		8
		43
		34
		20
		35
		22
		39
		13