seeplusplus
Advent of Code 2024 - Day 7
This one was much easier for me than yesterday’s. Part 1 runs in 22ms and part 2 runs in ~3s.
defmodule BridgeRepair do
def parse_input(input) do
input
|> String.trim()
|> String.split("\n")
|> Stream.map(fn l ->
[acc, nums] = String.split(l, ":")
nums = nums |> String.trim() |> String.split(" ") |> Enum.map(&String.to_integer/1)
{acc |> String.to_integer(), nums}
end)
end
def combine_ints(acc, [], _), do: acc
def combine_ints(acc, [i | rest], ops) do
ops
|> Enum.flat_map(fn op ->
acc |> Enum.map(fn j ->
case op do
:plus -> j + i
:mul -> j * i
:cat -> "#{j}#{i}" |> String.to_integer()
end
end)
end)
|> combine_ints(rest, ops)
end
def part_one_ops() do
[:plus, :mul]
end
def part_two_ops() do
[:cat | part_one_ops()]
end
def solve(input, part) do
input
|> BridgeRepair.parse_input()
|> Stream.filter(fn {sum, [i | rest]} ->
BridgeRepair.combine_ints(
[i],
rest,
(if part == :part1, do: part_one_ops(), else: part_two_ops())
) |> Enum.any?(&(&1 == sum))
end)
|> Stream.map(fn {i, _} -> i end)
|> Enum.sum
end
end
Edit small optimization on the concat operation:
:cat -> j*10**(i |> Integer.digits() |> Enum.count) + i
reduces part 2 runtime to 800ms.
Most Liked
sevenseacat
Author of Ash Framework
Much easier than yesterday! I still went through a few iterations before landing on this one:
https://github.com/sevenseacat/advent_of_code/blob/main/lib/y2024/day07.ex
This takes about 250ms to run on my machine for part 2.
My aim for this year is to have each solution run in less than a second - we’ll see how far I get lol
3
billylanchantin
LOC: 11
defmodule Aoc2024.Day07 do
def part1(file), do: main(file, [&+/2, &*/2])
def part2(file), do: main(file, [&+/2, &*/2, &concat/2])
def main(file, fs), do: file |> f2ls(&p/1) |> Enum.reduce(0, &(&2 + value(&1, fs)))
def f2ls(f, fun), do: f |> File.read!() |> String.trim() |> String.split("\n") |> Enum.map(fun)
def p(l), do: l |> String.replace(":", "") |> String.split() |> Enum.map(&String.to_integer/1)
def value([out, in1 | rest], fs), do: if(search?(out, in1, rest, fs), do: out, else: 0)
def search?(out, acc, [], _), do: out == acc
def search?(out, acc, [h | t], fs), do: Enum.any?(fs, &search?(out, &1.(acc, h), t, fs))
def concat(a, b), do: Integer.undigits(Integer.digits(a) ++ Integer.digits(b))
end
In my actual solution, f2ls and p are better named via an import:
import Aoc2024.Util
#...
def main(file, fs), do: file |> file_to_lines(&parse/1) |> Enum.reduce(0, &(&2 + value(&1, fs)))
def parse(line), do: line |> String.replace(":", "") |> line_to_list_of_ints
But that bumps up the line count.
3
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