Day 2

lib/day2/day2.ex

@@ -0,0 +1,67 @@
+defmodule Day2 do
+  def read_program do
+    File.read!("lib/day2/input.txt")
+    |> String.trim()
+    |> String.split(",")
+    |> Enum.map(&String.to_integer/1)
+  end
+
+  def part1 do
+    read_program()
+    |> List.replace_at(1, 12)
+    |> List.replace_at(2, 2)
+    |> run()
+  end
+
+  def part2 do
+    base_prog = read_program()
+
+    Enum.each(0..99, fn a ->
+      Enum.each(0..99, fn b ->
+        res =
+          base_prog
+          |> List.replace_at(1, a)
+          |> List.replace_at(2, b)
+          |> run()
+
+        if Enum.at(res, 0) == 19_690_720 do
+          IO.inspect(100 * a + b)
+        end
+      end)
+    end)
+  end
+
+  def run(memory, ip \\ 0)
+
+  def run(memory, ip) when ip < length(memory) do
+    case eval(Enum.drop(memory, ip), memory) do
+      {:halt, memory} ->
+        memory
+
+      {:cont, memory, offset} ->
+        run(memory, ip + offset)
+    end
+  end
+
+  def run(memory, _ip), do: memory
+
+  def eval([99 | _], memory) do
+    {:halt, memory}
+  end
+
+  def eval([1, a, b, dest | _], memory) do
+    {
+      :cont,
+      List.replace_at(memory, dest, Enum.at(memory, a) + Enum.at(memory, b)),
+      4
+    }
+  end
+
+  def eval([2, a, b, dest | _], memory) do
+    {
+      :cont,
+      List.replace_at(memory, dest, Enum.at(memory, a) * Enum.at(memory, b)),
+      4
+    }
+  end
+end

lib/day2/input.txt

@@ -0,0 +1 @@
+1,0,0,3,1,1,2,3,1,3,4,3,1,5,0,3,2,10,1,19,1,19,5,23,1,23,9,27,2,27,6,31,1,31,6,35,2,35,9,39,1,6,39,43,2,10,43,47,1,47,9,51,1,51,6,55,1,55,6,59,2,59,10,63,1,6,63,67,2,6,67,71,1,71,5,75,2,13,75,79,1,10,79,83,1,5,83,87,2,87,10,91,1,5,91,95,2,95,6,99,1,99,6,103,2,103,6,107,2,107,9,111,1,111,5,115,1,115,6,119,2,6,119,123,1,5,123,127,1,127,13,131,1,2,131,135,1,135,10,0,99,2,14,0,0