add day2 2024

elixir/livebook/2024/day2.livemd

@@ -0,0 +1,55 @@
+# Day 2 AOC 2024
+
+```elixir
+Mix.install([
+  {:nx, "0.9.2"},
+  {:req, "0.5.8"}
+])
+```
+
+## Section
+
+
+
+```elixir
+input = """
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9
+"""
+```
+
+```elixir
+is_safe? = fn report ->
+  differences = report 
+    |> Stream.chunk_every(2, 1, :discard) 
+    |> Enum.map(fn [a, b] -> a - b end) 
+  is_monotone? = differences |> Enum.all?(&(&1 < 0)) or differences |> Enum.all?(&(&1 > 0))
+  is_gradual? = differences |> Stream.map(&(abs(&1))) |> Enum.all?(&(&1 >= 1 and &1 <= 3))
+  is_monotone? and is_gradual?
+end
+```
+
+```elixir
+can_be_dampened? = fn report ->
+  Stream.with_index(report) |> Enum.any?(fn {_,i} ->
+    List.delete_at(report, i) |> is_safe?.()
+  end)
+end
+```
+
+```elixir
+for line <- input |> String.trim() |> String.split("\n") do
+  for c <- line |> String.split(" "),
+    c = c |> String.to_integer() do
+    c
+  end
+end
+|> Stream.filter(fn report -> 
+  is_safe?.(report) # or can_be_dampened?.(report)
+end)
+|> Enum.count
+```