add day5 aoc 2024

elixir/livebook/2024/day5.livemd

@@ -0,0 +1,58 @@
+# AOC 2024 Day 5
+
+## Section
+
+```elixir
+input = """
+"""
+```
+
+```elixir
+[rules, updates] = input |> String.split("\n\n")
+```
+
+```elixir
+rules = for rule <- rules |> String.split("\n"),
+    [a, b] = rule |> String.split("|"),
+    a = String.to_integer(a),
+    b = String.to_integer(b)
+  do
+  {a, b}
+end
+```
+
+```elixir
+updates = for update <- updates |> String.trim() |> String.split("\n"),
+  update = update |> String.trim() |> String.split(",") do
+    for page <- update,
+      page = String.to_integer(page) do
+      page
+    end
+  end
+```
+
+```elixir
+rule_sorter = fn a, b ->
+  a_precedes_b = Enum.any?(rules, &(&1 == {a, b}))
+  b_precedes_a = Enum.any?(rules, &(&1 == {b, a}))
+  cond do 
+    b_precedes_a -> false
+    a_precedes_b -> true
+    true -> true
+  end
+end
+```
+
+```elixir
+for update <- updates,
+  sorted = Enum.sort(update, rule_sorter),
+  sorted != update,
+  reduce: 0 do
+  acc -> 
+    len = sorted |> Enum.count
+    mid_idx = floor(len / 2)
+    acc + Enum.at(sorted, mid_idx)
+end
+
+# 10495 too high
+```