From 44c277ff94b615ab24d77b68108c2ff49a0aca9d Mon Sep 17 00:00:00 2001
From: sloane <1699281+sloanelybutsurely@users.noreply.github.com>
Date: Fri, 8 Dec 2023 12:49:55 -0500
Subject: [PATCH] solve 2023 8.2
---
2023/lib/2023/8.ex | 36 ++++++++++++++++++++++++++++++------
README.md | 2 +-
2 files changed, 31 insertions(+), 7 deletions(-)
diff --git a/2023/lib/2023/8.ex b/2023/lib/2023/8.ex
index c6d37a1..40bffa5 100644
--- a/2023/lib/2023/8.ex
+++ b/2023/lib/2023/8.ex
@@ -5,20 +5,40 @@ aoc 2023, 8 do
def p1(input) do
{instructions, mappings} = read_input(input)
- start = "AAA"
- finish = "ZZZ"
-
all_but_last_step =
instructions
|> Stream.cycle()
- |> Stream.scan(start, &step(&1, &2, mappings))
- |> Stream.take_while(&(&1 != finish))
+ |> Stream.scan("AAA", &step(&1, &2, mappings))
+ |> Stream.take_while(&(&1 != "ZZZ"))
|> Enum.count()
all_but_last_step + 1
end
- def p2(_input) do
+ def p2(input) do
+ {instructions, mappings} = read_input(input)
+
+ starts =
+ mappings
+ |> Map.keys()
+ |> Enum.filter(&String.ends_with?(&1, "A"))
+
+ lengths =
+ starts
+ |> Enum.map(fn start ->
+ n =
+ instructions
+ |> Stream.cycle()
+ |> Stream.scan(start, &step(&1, &2, mappings))
+ |> Stream.take_while(&(not String.ends_with?(&1, "Z")))
+ |> Enum.count()
+
+ n + 1
+ end)
+
+ Enum.reduce(lengths, fn a, b ->
+ div(a * b, Integer.gcd(a, b))
+ end)
end
def step("L", curr, mappings) do
@@ -33,6 +53,10 @@ aoc 2023, 8 do
|> elem(1)
end
+ def step_all(inst, currs, mappings) do
+ Enum.map(currs, &step(inst, &1, mappings))
+ end
+
def read_input(input) do
[instructions_string, _ | mapping_lines] = lines(input)
instructions = letters(instructions_string)
diff --git a/README.md b/README.md
index ed36e90..d5cc989 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@
1. [2020] **17/50** 🌟
1. [2021] **43/50** 🌟
1. [2022] **14/50** 🌟
-1. [2023] **12/50** 🌟
+1. [2023] **13/50** 🌟
[2015]: ./2015
[2017]: ./2017