groovyda
Advent of Code 2022 - Day 5
Today’s challenge for me was about using reduce:
defmodule Prob5 do
def move([[h1 | rest] = _list1, list2]) do
[rest, [h1 | list2]]
end
def move_n([l1, l2], n) do
Enum.reduce(1..n, [l1, l2], fn _, acc -> move(acc) end)
end
def single_instruction(input, [n, from_ind, to_ind], move_function) do
from_ind = from_ind - 1
to_ind = to_ind - 1
[from, to] = move_function.([Enum.at(input, from_ind), Enum.at(input, to_ind)], n)
input
|> List.replace_at(from_ind, from)
|> List.replace_at(to_ind, to)
end
def parse_line(line) do
[[n], [from_ind], [to_ind]] = Regex.scan(~r/\d+/, line)
Enum.map([n, from_ind, to_ind], &String.to_integer/1)
end
def move_n_part2([l1, l2], n) do
to_move = Enum.take(l1, n)
[Enum.drop(l1, n), to_move ++ l2]
end
end
I manually parsed the first part of the input into lists, like thus:
test_input = [[:n, :z], [:d, :c, :m], [:p]]
And then parsed the 2nd part of the input into simple lists, and finally ran it through reduce:
Enum.reduce(
instructions,
input,
fn instruction, input -> Prob5.single_instruction(input, instruction, &Prob5.move_n/2) end)
… using the 2 move functions - one for each part.
Let me know how this can be improved!
Thanks
Most Liked
mudasobwa
As always, I am here to advertise Access.
# moving crates (part I)
Enum.reduce(0..count - 1, acc, fn _, acc ->
{v, acc} = get_and_update_in(acc, [Access.at(from - 1)], fn [h|t] -> {h, t} end)
update_in(acc, [Access.at(to - 1)], fn t -> [v|t] end)
end)
# moving crates (part II)
{v, acc} = get_and_update_in(acc, [Access.at(from - 1)], fn l -> Enum.split(l, count) end)
update_in(acc, [Access.at(to - 1)], fn t -> v ++ t end)
mudasobwa
mudasobwa
Finite number of moves is a synonym of reduce/3 through 
adamu
I thought about Access but I thought, “piles of crates with an index” sounds like a map!
Just throwing mine into the mix.
defp move_9000(0, from, to), do: {from, to}
defp move_9000(number, [crate | from], to), do: move_9000(number - 1, from, [crate | to])
defp move_9001(number, from, to) do
{moving, moved_from} = Enum.split(from, number)
{moved_from, moving ++ to}
end
Completing in <100μs so can’t be too bad
mudasobwa
I could not disagree more.
Oh, wait, I could.
Access is something I use in each and every project, I even created the library to inject a performant Access implementation into home-baked structs (estructura.) Also anyone who dealt with deeply nested structures at least once, would use it again and again for its simplicity, elegance and uniformness.
Popular in Challenges
Other popular topics
Latest on Elixir Forum
Sponsor Spotlight
Courses that'll move you from confusion to "Aha, now I get it!"
Categories:
Sub Categories:
Forums
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Practical resources that improve the lives of professional developers.
Develop your skills with books, videos, and courses.
The deployment platform built for Elixir: PaaS ease, VPS control.
Courses that'll move you from confusion to "Aha, now I get it!"