<!-- livebook:{"hub_id":"team-weiz"} -->
# Day09
## Section
```elixir
example = "2333133121414131402"
defmodule Day09 do
def parse_input(input) do
input
|> String.split("", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.chunk_every(2)
|> Enum.with_index(fn
[f], i -> List.duplicate(to_string(i), f)
[f, s], i -> [List.duplicate(to_string(i), f), List.duplicate(".", s)]
end)
|> List.flatten()
end
def part1(raw_input) do
input = parse_input(raw_input)
length = Enum.count(input, &(&1 != "."))
rearrange(input, Enum.reverse(input), [], length)
|> Enum.with_index(fn e, i -> String.to_integer(e) * i end)
|> Enum.sum()
end
def rearrange(_, _, acc, l) when length(acc) == l, do: Enum.reverse(acc)
def rearrange(i, ["." | rt], acc, l), do: rearrange(i, rt, acc, l)
def rearrange(["." | it], [rh | rt], acc, l), do: rearrange(it, rt, [rh | acc], l)
def rearrange([ih | it], r, acc, l), do: rearrange(it, r, [ih | acc], l)
def parse_input2(input) do
input
|> String.split("", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.chunk_every(2)
|> Enum.with_index(fn
[f], i -> {f, i}
[f, s], i -> [{f, i}, {s, "."}]
end)
|> Enum.reduce([], fn
[a, b], acc -> [b | [a | acc]]
last, acc -> [last | acc]
end)
|> Enum.reverse()
end
def part2(raw_input) do
input = parse_input2(raw_input)
merge(input)
|> Enum.map(fn {size, i} -> List.duplicate(i, size) end)
|> List.flatten()
|> Enum.with_index(fn
".", _i -> 0
e, i -> e * i
end)
|> Enum.sum()
end
def merge(input) do
input
|> Enum.reverse()
|> Enum.reject(&(elem(&1, 1) == "."))
|> Enum.reduce(input, fn {size, data}, list ->
list
|> move_item({size, data})
|> Enum.reverse()
|> merge_gaps()
end)
end
def move_item(list, {size, data}) do
Enum.reduce(list, {[], :find}, fn
{slot_size, "."}, {items, :find} ->
cond do
slot_size > size ->
{[{slot_size - size, "."} | [{size, data} | items]], :hit}
slot_size == size ->
{[{size, data} | items], :hit}
true ->
{[{slot_size, "."} | items], :find}
end
{^size, ^data}, {items, :hit} ->
{[{size, "."} | items], :hit}
{^size, ^data}, {items, :find} ->
{[{size, data} | items], :hit}
item, {items, status} ->
{[item | items], status}
end)
|> elem(0)
end
def merge_gaps(list) do
list
|> merge_gaps([])
|> Enum.reverse()
end
def merge_gaps([], acc), do: acc
def merge_gaps([{h1s, "."}, {h2s, "."}], acc), do: [{h1s + h2s, "."} | acc]
def merge_gaps([h1, h2], acc), do: [h2 | [h1 | acc]]
def merge_gaps([{h1s, "."} | [{h2s, "."} | rest]], acc),
do: merge_gaps(rest, [{h1s + h2s, "."} | acc])
def merge_gaps([h | rest], acc), do: merge_gaps(rest, [h | acc])
end
Day09.part1(example)
Day09.part2(example)
```
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