1 files changed, 74 insertions, 0 deletions
diff --git a/src/day10.exs b/src/day10.exs
new file mode 100644
index 0000000..7530903
--- /dev/null
+++ b/src/day10.exs
@@ -0,0 +1,74 @@
+defmodule Day10 do
+  def part1(data) do
+    grid = data
+    |> String.split("\n", trim: true)
+    |> Enum.map(&String.codepoints/1)
+    |> Enum.map(fn v -> Enum.map(v, &String.to_integer/1) end)
+
+    values = for {l, i} <- Enum.with_index(grid),
+                 {v, j} <- Enum.with_index(l) do
+               {v, {i, j}}
+    end
+    |> Enum.group_by(fn {v, _} -> v end, fn {_, p} -> p end)
+
+    dist = fn {a, b}, {c, d} -> abs(a-c) + abs(b-d) end
+    ends = fn p, prev ->
+      for {_, v} <- Enum.filter(prev, fn {p2, _} -> dist.(p, p2) == 1 end),
+          reduce: MapSet.new() do
+        acc -> MapSet.union(acc, v)
+      end
+    end
+
+    for i <- 8..0//-1,
+        reduce: Map.get(values, 9, []) |> Enum.map(& {&1, MapSet.new([&1])}) do
+      acc -> Map.get(values, i, [])
+      |> Enum.map(fn p -> {p, ends.(p, acc)} end)
+      |> Enum.filter(fn {_, m} -> MapSet.size(m) > 0 end)
+    end
+    |> Enum.map(fn {_, m} -> MapSet.size(m) end)
+    |> Enum.sum()
+  end
+
+  def part2(data) do
+    grid = data
+    |> String.split("\n", trim: true)
+    |> Enum.map(&String.codepoints/1)
+    |> Enum.map(fn v -> Enum.map(v, &String.to_integer/1) end)
+
+    values = for {l, i} <- Enum.with_index(grid),
+                 {v, j} <- Enum.with_index(l) do
+               {v, {i, j}}
+    end
+    |> Enum.group_by(fn {v, _} -> v end, fn {_, p} -> p end)
+
+    acc = values
+    |> Map.get(9, [])
+    |> Enum.map(fn p -> {p, 1} end)
+
+    dist = fn {a, b}, {c, d} -> abs(a-c) + abs(b-d) end
+    count = fn p, prev ->
+      prev
+      |> Enum.filter(fn {p2, _} -> dist.(p, p2) == 1 end)
+      |> Enum.map(fn {_, c} -> c end)
+      |> Enum.sum()
+    end
+
+    for i <- 8..0//-1, reduce: acc do
+      acc -> Map.get(values, i, [])
+      |> Enum.map(fn p -> {p, count.(p, acc)} end)
+      |> Enum.filter(fn {_, c} -> c > 0 end)
+    end
+    |> Enum.map(fn {_, c} -> c end)
+    |> Enum.sum()
+  end
+end
+
+data = IO.read(:stdio, :eof)
+
+{time1 , ans1} = :timer.tc(fn -> Day10.part1(data) end)
+IO.puts("Time  : #{time1 / 1000000}")
+IO.puts("Answer: #{ans1}")
+
+{time2 , ans2} = :timer.tc(fn -> Day10.part2(data) end)
+IO.puts("Time  : #{time2 / 1000000}")
+IO.puts("Answer: #{ans2}")