Day 9

1 files changed, 95 insertions, 0 deletions

diff --git a/src/day09.exs b/src/day09.exs
new file mode 100644
index 0000000..1e37cad
--- /dev/null
+++ b/src/day09.exs
@@ -0,0 +1,95 @@
+defmodule Day09 do
+  def part1(data) do
+    values = data
+    |> String.split("\n", trim: true)
+    |> hd()
+    |> String.codepoints()
+    |> Enum.map(& String.to_integer/1)
+
+    files = values
+    |> Enum.take_every(2)
+    |> Enum.with_index()
+    |> Enum.flat_map(fn {v, i} -> Stream.cycle([i]) |> Enum.take(v) end)
+
+    revfiles = files
+    |> Enum.reverse()
+
+    v2 = values
+    |> Enum.with_index()
+    |> Enum.flat_map(fn {v, i} -> Stream.cycle([i]) |> Enum.take(v) end)
+    |> Enum.with_index()
+
+    c1 = v2
+    |> Enum.filter(fn {i, _} -> rem(i, 2) == 0 end)
+    |> Enum.zip(files)
+
+    c2 = v2
+    |> Enum.filter(fn {i, _} -> rem(i, 2) == 1 end)
+    |> Enum.zip(revfiles)
+
+    (c1 ++ c2)
+    |> Enum.sort_by(fn {{_, i}, _} -> i end)
+    |> Enum.take(Enum.count(files))
+    |> Enum.map(fn {{_, i}, v} -> i*v end)
+    |> Enum.sum()
+  end
+
+  def part2(data) do
+    values = data
+    |> String.split("\n", trim: true)
+    |> hd()
+    |> String.codepoints()
+    |> Enum.map(& String.to_integer/1)
+    |> Enum.scan({0, 0}, fn v, {o, i} -> {v, o+i} end)
+
+    spaces = values
+    |> tl()
+    |> Enum.take_every(2)
+
+    values
+    |> Enum.take_every(2)
+    |> Enum.with_index()
+    |> Enum.reverse()
+    |> locations(spaces)
+    |> Enum.map(fn {a, b, i} -> i*Enum.sum(b..b+a-1) end)
+    |> Enum.sum()
+  end
+
+  defp locations(acc \\ [], revfiles, spaces)
+
+  defp locations(acc, [{{a, b}, i} | t], spaces) do
+    spaces = Enum.filter(spaces, fn {_, d} -> d < b end)
+
+    s = spaces
+    |> Enum.filter(fn {c, _} -> c >= a end)
+    |> Enum.min_by(fn {_, d} -> d end, &<=/2, fn -> nil end)
+
+    if s == nil do
+      locations([{a, b, i} | acc], t, spaces)
+    else
+      spaces = List.delete(spaces, s)
+      {c, d} = s
+      spaces =
+        if c == a do
+          spaces
+        else
+          [{c-a, d+a} | spaces]
+        end
+      locations([{a, d, i} | acc], t, spaces)
+    end
+  end
+
+  defp locations(acc, [], _) do
+    acc
+  end
+end
+
+data = IO.read(:stdio, :eof)
+
+{time1 , ans1} = :timer.tc(fn -> Day09.part1(data) end)
+IO.puts("Time  : #{time1 / 1000000}")
+IO.puts("Answer: #{ans1}")
+
+{time2 , ans2} = :timer.tc(fn -> Day09.part2(data) end)
+IO.puts("Time  : #{time2 / 1000000}")
+IO.puts("Answer: #{ans2}")