From 7a46852b2360b661375045d64de5db477678e4cc Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Fri, 18 Dec 2020 18:13:33 +0900
Subject: [PATCH] Simplify

---
 day18/day18part1.exs | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/day18/day18part1.exs b/day18/day18part1.exs
index 878a211..e8f0e1b 100644
--- a/day18/day18part1.exs
+++ b/day18/day18part1.exs
@@ -12,27 +12,19 @@ defmodule Day18Part1 do
     |> String.graphemes()
     |> Stream.reject(fn char -> char in [" ", "\n"] end)
     |> Enum.map(fn
-      "*" -> :multiply
-      "+" -> :add
-      "(" -> :start_group
-      ")" -> :end_group
+      symbol when symbol in ["*", "+", "(", ")"] -> symbol
       num -> String.to_integer(num)
     end)
   end
 
   def evaluate(command), do: evaluate(command, nil, 0)
   def evaluate([], nil, acc), do: acc
-  def evaluate([:multiply | rest], nil, acc), do: evaluate(rest, :multiply, acc)
-  def evaluate([:add | rest], nil, acc), do: evaluate(rest, :add, acc)
-
-  def evaluate([:start_group | rest], op, acc) do
-    {remaining, group_result} = evaluate(rest, nil, 0)
-    evaluate([group_result | remaining], op, acc)
-  end
-
-  def evaluate([:end_group | rest], _op, acc), do: {rest, acc}
-  def evaluate([num | rest], :multiply, acc), do: evaluate(rest, nil, acc * num)
-  def evaluate([num | rest], :add, acc), do: evaluate(rest, nil, acc + num)
+  def evaluate(["*" | rest], nil, acc), do: evaluate(rest, "*", acc)
+  def evaluate(["+" | rest], nil, acc), do: evaluate(rest, "+", acc)
+  def evaluate(["(" | rest], op, acc), do: evaluate(rest) |> evaluate(op, acc)
+  def evaluate([")" | rest], nil, acc), do: [acc | rest]
+  def evaluate([num | rest], "*", acc), do: evaluate(rest, nil, acc * num)
+  def evaluate([num | rest], "+", acc), do: evaluate(rest, nil, acc + num)
   def evaluate([num | rest], nil, 0), do: evaluate(rest, nil, num)
 end