# Day12
## Untitled
<!-- livebook:{"livebook_object":"cell_input","name":"input","type":"textarea","value":"bm-XY\nol-JS\nbm-im\nRD-ol\nbm-QI\nJS-ja\nim-gq\nend-im\nja-ol\nJS-gq\nbm-AF\nRD-start\nRD-ja\nstart-ol\ncj-bm\nstart-JS\nAF-ol\nend-QI\nQI-gq\nja-gq\nend-AF\nim-QI\nbm-gq\nja-QI\ngq-RD\n"} -->
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
data =
"input"
|> IO.getn(1_000_000)
|> String.trim()
|> String.split(["\n", "\r\n"], trim: true)
|> Enum.map(&String.split(&1, "-"))
data =
for [from, to] <- data do
[{from, to}, {to, from}]
end
|> List.flatten()
|> Enum.reject(fn {from, to} -> from == "end" or to == "start" end)
|> Enum.group_by(fn {f, _t} -> f end, fn {_f, t} -> t end)
```
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
defmodule P1 do
def calc(from, data, seen) do
next = data[from]
seen =
if match?(<<c::8, _::binary>> when c in ?a..?z, from) do
[from | seen]
else
seen
end
next
|> Kernel.--(seen)
|> Enum.reduce(0, fn
"end", sum ->
sum + 1
next, sum ->
sum + calc(next, data, seen)
end)
end
end
```
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
P1.calc("start", data, [])
```
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
defmodule P2 do
def calc(from, data, seen, exception) do
seen =
if match?(<<c::8, _::binary>> when c in ?a..?z, from) do
[from | seen]
else
seen
end
exception = exception && Enum.count_until(seen, &(&1 == from), 2) <= 1
next = data[from] -- if(exception, do: [], else: seen)
Enum.reduce(next, 0, fn
"end", sum ->
sum + 1
next, sum ->
sum + calc(next, data, seen, exception)
end)
end
end
```
<!-- livebook:{"reevaluate_automatically":true} -->
```elixir
P2.calc("start", data, [], true)
```
