# Day 11
## Part 1
```elixir
# input = "125 17"
input = "2 77706 5847 9258441 0 741 883933 12"
```
```elixir
defmodule U do
def parse(input) do
input |> String.split() |> Enum.map(&String.to_integer/1)
end
end
```
```elixir
stones = U.parse(input)
```
```elixir
defmodule P1 do
require Integer
def steps(stones), do: steps(stones, 25)
def steps(stones, 0), do: Enum.count(stones)
def steps(stones, i) do
step(stones) |> steps(i - 1)
end
def step(stones) do
for stone <- stones,
stones = rule1(stone) || rule2(stone) || rule3(stone),
stone <- stones do
stone
end
end
def rule1(0), do: [1]
def rule1(_), do: nil
def rule2(stone) do
s = Integer.to_string(stone)
l = String.length(s)
if Integer.is_even(l) do
[
String.slice(s, 0, div(l, 2)) |> String.to_integer(),
String.slice(s, div(l, 2), div(l, 2)) |> String.to_integer()
]
end
end
def rule3(stone), do: [stone * 2024]
end
```
```elixir
P1.steps(stones)
```
## Part 2
```elixir
defmodule P2 do
require Integer
def steps(stones), do: steps(Map.from_keys(stones, 1), 75)
def steps(stones, 0), do: Map.values(stones) |> Enum.sum()
def steps(stones, i) do
# IO.inspect({25 - i, Map.values(stones) |> Enum.sum(), stones})
Enum.reduce(stones, %{}, fn {n, c}, m ->
u = fn x -> x + c end
s = Integer.to_string(n)
l = String.length(s)
cond do
n == 0 ->
Map.update(m, 1, c, u)
Integer.is_even(l) ->
h = div(l, 2)
m
|> Map.update(String.slice(s, 0, h) |> String.to_integer(), c, u)
|> Map.update(String.slice(s, h, h) |> String.to_integer(), c, u)
true ->
Map.update(m, n * 2024, c, u)
end
end)
|> steps(i - 1)
end
end
```
```elixir
P2.steps(stones)
```
