add 2024/11

elixir/livebook/2024/day11.livemd

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+# AOC 2024 Day 11
+
+## Section
+
+```elixir
+input = """
+""" |> String.trim()
+
+```
+
+```elixir
+defmodule Blink do
+  def blink(stones) do
+    blink(stones |> Map.to_list(), %{})
+  end
+
+  def blink([], acc), do: acc
+
+  def blink([{0, n} | rest], acc) do
+    blink(rest, acc |> Map.update(1, n, &(&1 + n)))
+  end
+
+  def blink([{stone, n} | rest], acc) do
+    case even_digits?(stone) do
+      {true, x} ->
+        left = left(stone, div(x, 2))
+        right = stone - shift_left(left, div(x, 2))
+
+        blink(
+          rest,
+          acc
+          |> Map.update(left, n, &(&1 + n))
+          |> Map.update(right, n, &(&1 + n))
+        )
+
+      _ ->
+        blink(
+          rest,
+          acc |> Map.update(stone * 2024, n, &(&1 + n))
+        )
+    end
+  end
+
+  def split_n(n, m) do
+    {left(n, m), right(n, m)}
+  end
+
+  def left(n, 0), do: n
+
+  def left(n, m) do
+    left(div(n, 10), m - 1)
+  end
+
+  def right(n, m) do
+    left = left(n, m)
+    right = n - shift_left(left, m)
+    right
+  end
+
+  def shift_left(n, 0), do: n
+
+  def shift_left(n, m) do
+    shift_left(n * 10, m - 1)
+  end
+
+  def even_digits?(0), do: {false, 1}
+
+  def even_digits?(n) do
+    even_digits?(n, 0)
+  end
+
+  def even_digits?(0, a), do: {rem(a, 2) == 0, a}
+  def even_digits?(n, a), do: even_digits?(div(n, 10), a + 1)
+
+  def solve(input, n) do
+    input = input |> String.split(" ") |> Enum.map(&String.to_integer/1) |> Enum.frequencies()
+    for _ <- 1..n, reduce: input do
+      acc -> Blink.blink(acc)
+    end
+    |> Map.values()
+    |> Enum.sum()
+  end
+
+  def part1(input), do: solve(input, 25)
+  def part2(input), do: solve(input, 75)
+end
+```
+
+```elixir
+Blink.part1(input)
+```
+
+```elixir
+Blink.part2(input)
+```