add day 1 solutions

day1/day1.exs

@@ -0,0 +1,10 @@
+# input treatment
+input = IO.gets("input?")
+        |> String.trim
+        |> String.split(" ")
+        |> Enum.map(fn part ->
+          String.to_integer part
+        end)
+
+res = Enum.sum(input)
+IO.puts "answer: #{res}"

day1/day1_2.exs

@@ -0,0 +1,64 @@
+input = IO.gets("input?")
+        |> String.trim
+        |> String.split(" ")
+        |> Enum.map(fn part ->
+          String.to_integer part
+        end)
+
+defmodule Day1_2 do
+  def pass(input, state) do
+
+    # pass through the entire list with reduce
+    # so we have some kind of state in acc
+    result = Enum.reduce(input, state, fn part, acc ->
+      case acc do
+
+        # if we already found it, we don't need
+        # to keep iterating
+        {:ok, res} ->
+          {:ok, res}
+
+        # acc grows like this:
+        # [0]
+        # [0 + first_change | 0]
+
+        # [0 + first_change + second_change |
+        # [0 + first_change | 0]], etc
+        [current | _rest] ->
+          # the head of the list is the current
+          # frequency of the device that we'll
+          # apply the change to (part)
+          new_freq = current + part
+
+          # then we search in the OLD list
+          # if we are a member of it
+          #
+          # if we are, then we are actually the first
+          # repeated frequency in the list.
+          became_member = Enum.member?(acc, new_freq)
+
+          if became_member do
+            # this should make the reduce()
+            # call stop creating new frequencies
+            # and just returning what it found
+            {:ok, new_freq}
+          else
+            # if we didn't find, we add the new frequency
+            # to the list, and keep going.
+            [new_freq | acc]
+          end
+      end
+    end)
+
+    case result do
+      {:ok, res} -> res
+
+        # if
+      _ -> pass(input, result)
+    end
+  end
+end
+
+res = Day1_2.pass(input, [0])
+
+IO.puts "total res: #{inspect res}"