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Commit 0be2dad

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solution day 8
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‎CMakeLists.txt‎

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@@ -13,3 +13,4 @@ add_subdirectory ("day04")
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add_subdirectory ("day05")
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add_subdirectory ("day06")
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add_subdirectory ("day07")
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add_subdirectory ("day08")

‎day08/CMakeLists.txt‎

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cmake_minimum_required (VERSION 3.27)
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get_filename_component (CURRENT_DAY ${CMAKE_CURRENT_SOURCE_DIR} NAME)
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configure_file("input.txt" "input.txt" COPYONLY)
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add_executable (${CURRENT_DAY}part1 "part1.cpp" )
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add_executable (${CURRENT_DAY}part2 "part2.cpp" )
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set_property(TARGET ${CURRENT_DAY}part1 PROPERTY CXX_STANDARD 23)
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set_property(TARGET ${CURRENT_DAY}part1 PROPERTY CMAKE_CXX_STANDARD_REQUIRED YES)
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set_property(TARGET ${CURRENT_DAY}part2 PROPERTY CXX_STANDARD 23)
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set_property(TARGET ${CURRENT_DAY}part2 PROPERTY CMAKE_CXX_STANDARD_REQUIRED YES)

‎day08/README.md‎

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# Day 8: Haunted Wasteland
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[https://adventofcode.com/2023/day/8](https://adventofcode.com/2023/day/8)
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## Description
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### Part One
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You're still riding a camel across Desert Island when you spot a sandstorm quickly approaching. When you turn to warn the Elf, she disappears before your eyes! To be fair, she had just finished warning you about _ghosts_ a few minutes ago.
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One of the camel's pouches is labeled "maps" - sure enough, it's full of documents (your puzzle input) about how to navigate the desert. At least, you're pretty sure that's what they are; one of the documents contains a list of left/right instructions, and the rest of the documents seem to describe some kind of _network_ of labeled nodes.
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It seems like you're meant to use the _left/right_ instructions to _navigate the network_. Perhaps if you have the camel follow the same instructions, you can escape the haunted wasteland!
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After examining the maps for a bit, two nodes stick out: `AAA` and `ZZZ`. You feel like `AAA` is where you are now, and you have to follow the left/right instructions until you reach `ZZZ`.
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This format defines each _node_ of the network individually. For example:
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RL
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AAA = (BBB, CCC)
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BBB = (DDD, EEE)
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CCC = (ZZZ, GGG)
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DDD = (DDD, DDD)
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EEE = (EEE, EEE)
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GGG = (GGG, GGG)
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ZZZ = (ZZZ, ZZZ)
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Starting with `AAA`, you need to _look up the next element_ based on the next left/right instruction in your input. In this example, start with `AAA` and go _right_ (`R`) by choosing the right element of `AAA`, _`CCC`_. Then, `L` means to choose the _left_ element of `CCC`, _`ZZZ`_. By following the left/right instructions, you reach `ZZZ` in _`2`_ steps.
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Of course, you might not find `ZZZ` right away. If you run out of left/right instructions, repeat the whole sequence of instructions as necessary: `RL` really means `RLRLRLRLRLRLRLRL...` and so on. For example, here is a situation that takes _`6`_ steps to reach `ZZZ`:
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LLR
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AAA = (BBB, BBB)
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BBB = (AAA, ZZZ)
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ZZZ = (ZZZ, ZZZ)
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Starting at `AAA`, follow the left/right instructions. _How many steps are required to reach `ZZZ`?_
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### Part Two
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The <span title="Duhduhduhduhduh! Dah, duhduhduhduhduh!">sandstorm</span> is upon you and you aren't any closer to escaping the wasteland. You had the camel follow the instructions, but you've barely left your starting position. It's going to take _significantly more steps_ to escape!
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What if the map isn't for people - what if the map is for _ghosts_? Are ghosts even bound by the laws of spacetime? Only one way to find out.
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After examining the maps a bit longer, your attention is drawn to a curious fact: the number of nodes with names ending in `A` is equal to the number ending in `Z`! If you were a ghost, you'd probably just _start at every node that ends with `A`_ and follow all of the paths at the same time until they all simultaneously end up at nodes that end with `Z`.
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For example:
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LR
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11A = (11B, XXX)
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11B = (XXX, 11Z)
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11Z = (11B, XXX)
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22A = (22B, XXX)
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22B = (22C, 22C)
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22C = (22Z, 22Z)
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22Z = (22B, 22B)
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XXX = (XXX, XXX)
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Here, there are two starting nodes, `11A` and `22A` (because they both end with `A`). As you follow each left/right instruction, use that instruction to _simultaneously_ navigate away from both nodes you're currently on. Repeat this process until _all_ of the nodes you're currently on end with `Z`. (If only some of the nodes you're on end with `Z`, they act like any other node and you continue as normal.) In this example, you would proceed as follows:
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* Step 0: You are at `11A` and `22A`.
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* Step 1: You choose all of the _left_ paths, leading you to `11B` and `22B`.
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* Step 2: You choose all of the _right_ paths, leading you to _`11Z`_ and `22C`.
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* Step 3: You choose all of the _left_ paths, leading you to `11B` and _`22Z`_.
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* Step 4: You choose all of the _right_ paths, leading you to _`11Z`_ and `22B`.
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* Step 5: You choose all of the _left_ paths, leading you to `11B` and `22C`.
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* Step 6: You choose all of the _right_ paths, leading you to _`11Z`_ and _`22Z`_.
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So, in this example, you end up entirely on nodes that end in `Z` after _`6`_ steps.
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Simultaneously start on every node that ends with `A`. _How many steps does it take before you're only on nodes that end with `Z`?_

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