Days 1 and 2

2 files changed, 56 insertions, 0 deletions

diff --git a/src/day01.exs b/src/day01.exs
new file mode 100644
index 0000000..b9b346d
--- /dev/null
+++ b/src/day01.exs
@@ -0,0 +1,20 @@
+[l1, l2] = IO.read(:stdio, :eof)
+|> String.split([" ", "\n"], trim: true)
+|> Enum.map(&String.to_integer/1)
+|> Enum.with_index()
+|> Enum.split_with(fn {_v, i} -> rem(i, 2) == 0 end)
+|> Tuple.to_list()
+|> Enum.map(fn l -> Enum.map(l, fn {v, _i} -> v end) end)
+|> Enum.map(&Enum.sort/1)
+
+ans1 = Enum.zip(l1, l2)
+|> Enum.map(fn {v1, v2} -> abs(v1 - v2) end)
+|> Enum.sum()
+
+IO.puts(ans1)
+
+c2 = Enum.frequencies(l2)
+
+ans2 = Enum.map(l1, &(&1 * Map.get(c2, &1, 0))) |> Enum.sum()
+
+IO.puts(ans2)
diff --git a/src/day02.exs b/src/day02.exs
new file mode 100644
index 0000000..ae7bfde
--- /dev/null
+++ b/src/day02.exs
@@ -0,0 +1,36 @@
+defmodule Day02 do
+  def parse_report(line) do
+    line
+    |> String.trim()
+    |> String.split(" ")
+    |> Enum.map(&String.to_integer/1)
+  end
+
+  def is_report_safe(report) do
+    diffs = report
+    |> Enum.chunk_every(2, 1, :discard)
+    |> Enum.map(fn [a, b] -> b - a end)
+
+    Enum.all?(diffs, fn x -> 1 <= x and x <= 3 end) or
+      Enum.all?(diffs, fn x -> -3 <= x and x <= -1 end)
+  end
+
+  def is_report_safe_with_dampener(report) do
+    is_report_safe(report) or
+      Enum.any?(0..Enum.count(report)-1,
+                fn i -> List.delete_at(report, i) |> is_report_safe() end)
+  end
+end
+
+reports = IO.stream(:stdio, :line)
+|> Enum.map(&Day02.parse_report/1)
+
+ans1 = reports
+|> Enum.count(&Day02.is_report_safe/1)
+
+IO.puts(ans1)
+
+ans2 = reports
+|> Enum.count(&Day02.is_report_safe_with_dampener/1)
+
+IO.puts(ans2)