Advent of Code 2022 - Day 4
Mix.install([
{:kino_aoc, "~> 0.1"}
])
Introduction
— Day 4: Camp Cleanup —
Space needs to be cleared before the last supplies can be unloaded from the ships, and so several Elves have been assigned the job of cleaning up sections of the camp. Every section has a unique ID number, and each Elf is assigned a range of section IDs.
However, as some of the Elves compare their section assignments with each other, they’ve noticed that many of the assignments overlap. To try to quickly find overlaps and reduce duplicated effort, the Elves pair up and make a big list of the section assignments for each pair (your puzzle input).
For example, consider the following list of section assignment pairs:
2-4,6-8
2-3,4-5
5-7,7-9
2-8,3-7
6-6,4-6
2-6,4-8
For the first few pairs, this list means:
-
Within the first pair of Elves, the first Elf was assigned sections
2-4
(sections2
,3
, and4
), while the second Elf was assigned sections6-8
(sections6
,7
,8
). - The Elves in the second pair were each assigned two sections.
-
The Elves in the third pair were each assigned three sections: one got sections
5
,6
, and7
, while the other also got7
, plus8
and9
.
This example list uses single-digit section IDs to make it easier to draw; your actual list might contain larger numbers. Visually, these pairs of section assignments look like this:
.234..... 2-4
.....678. 6-8
.23...... 2-3
...45.... 4-5
....567.. 5-7
......789 7-9
.2345678. 2-8
..34567.. 3-7
.....6... 6-6
...456... 4-6
.23456... 2-6
...45678. 4-8
Some of the pairs have noticed that one of their assignments fully contains the other. For example, 2-8
fully contains 3-7
, and 6-6
is fully contained by 4-6
. In pairs where one assignment fully contains the other, one Elf in the pair would be exclusively cleaning sections their partner will already be cleaning, so these seem like the most in need of reconsideration. In this example, there are 2
such pairs.
In how many assignment pairs does one range fully contain the other?
— Part Two —
It seems like there is still quite a bit of duplicate work planned. Instead, the Elves would like to know the number of pairs that overlap at all.
In the above example, the first two pairs (2-4,6-8
and 2-3,4-5
) don’t overlap, while the remaining four pairs (5-7,7-9
, 2-8,3-7
, 6-6,4-6
, and 2-6,4-8
) do overlap:
-
5-7,7-9
overlaps in a single section,7
. -
2-8,3-7
overlaps all of the sections3
through7
. -
6-6,4-6
overlaps in a single section,6
. -
2-6,4-8
overlaps in sections4
,5
, and6
.
So, in this example, the number of overlapping assignment pairs is 4
.
In how many assignment pairs do the ranges overlap?
Puzzle
{:ok, puzzle_input} =
KinoAOC.download_puzzle("2022", "4", System.fetch_env!("LB_AOC_SESSION"))
Parser
Code - Parser
defmodule Parser do
def parse(input) do
input
|> String.split("\n")
|> Enum.map(&String.split(&1, ~r/[,-]/))
|> Enum.map(fn pairs -> Enum.map(pairs, &String.to_integer(&1)) end)
end
end
Tests - Parser
ExUnit.start(autorun: false)
defmodule ParserTest do
use ExUnit.Case, async: true
import Parser
@input "2-4,6-8\n2-3,4-5\n5-7,7-9\n2-8,3-7\n6-6,4-6\n2-6,4-8"
@expected [[2, 4, 6, 8], [2, 3, 4, 5], [5, 7, 7, 9], [2, 8, 3, 7], [6, 6, 4, 6], [2, 6, 4, 8]]
test "parse test" do
actual = parse(@input)
assert actual == @expected
end
end
ExUnit.run()
Part One
Code - Part 1
defmodule PartOne do
def solve(input) do
IO.puts("--- Part One ---")
IO.puts("Result: #{run(input)}")
end
# [la-lb,ra-rb]
# la: left a, lb: left b, ra: right a, rb: right b"
def fully_contains([la, lb, ra, rb]) do
cond do
la <= ra and lb >= rb -> 1
la >= ra and lb <= rb -> 1
:else -> 0
end
end
def run(input) do
input
|> Parser.parse()
|> Enum.map(&fully_contains(&1))
|> Enum.sum()
end
end
Tests - Part 1
ExUnit.start(autorun: false)
defmodule PartOneTest do
use ExUnit.Case, async: true
import PartOne
@input "2-4,6-8\n2-3,4-5\n5-7,7-9\n2-8,3-7\n6-6,4-6\n2-6,4-8"
@expected 2
test "part one" do
actual = run(@input)
assert actual == @expected
end
end
ExUnit.run()
Solution - Part 1
PartOne.solve(puzzle_input)
Part Two
Code - Part 2
defmodule PartTwo do
def solve(input) do
IO.puts("--- Part Two ---")
IO.puts("Result: #{run(input)}")
end
# [la-lb,ra-rb] = [4-5,3-8]
# la: left a, lb: left b, ra: right a, rb: right b"
def overlap_all([la, lb, ra, rb]) do
cond do
lb >= ra and la <= rb -> 1
:else -> 0
end
end
def run(input) do
input
|> Parser.parse()
|> Enum.map(&overlap_all(&1))
|> Enum.sum()
end
end
Tests - Part 2
ExUnit.start(autorun: false)
defmodule PartTwoTest do
use ExUnit.Case, async: true
import PartTwo
@input "2-4,6-8\n2-3,4-5\n5-7,7-9\n2-8,3-7\n6-6,4-6\n2-6,4-8"
@expected 4
test "part two" do
actual = run(@input)
assert actual == @expected
end
end
ExUnit.run()
Solution - Part 2
PartTwo.solve(puzzle_input)