139 lines
5.7 KiB
Plaintext
139 lines
5.7 KiB
Plaintext
Advent of Code
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--- Day 7: The Sum of Its Parts ---
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You find yourself standing on a snow-covered coastline; apparently, you
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landed a little off course. The region is too hilly to see the North Pole
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from here, but you do spot some Elves that seem to be trying to unpack
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something that washed ashore. It's quite cold out, so you decide to risk
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creating a paradox by asking them for directions.
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"Oh, are you the search party?" Somehow, you can understand whatever Elves
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from the year 1018 speak; you assume it's Ancient Nordic Elvish. Could the
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device on your wrist also be a translator? "Those clothes don't look very
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warm; take this." They hand you a heavy coat.
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"We do need to find our way back to the North Pole, but we have higher
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priorities at the moment. You see, believe it or not, this box contains
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something that will solve all of Santa's transportation problems - at least,
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that's what it looks like from the pictures in the instructions." It doesn't
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seem like they can read whatever language it's in, but you can: "Sleigh kit.
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Some assembly required."
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"'Sleigh'? What a wonderful name! You must help us assemble this 'sleigh' at
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once!" They start excitedly pulling more parts out of the box.
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The instructions specify a series of steps and requirements about which
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steps must be finished before others can begin (your puzzle input). Each
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step is designated by a single letter. For example, suppose you have the
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following instructions:
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Step C must be finished before step A can begin.
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Step C must be finished before step F can begin.
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Step A must be finished before step B can begin.
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Step A must be finished before step D can begin.
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Step B must be finished before step E can begin.
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Step D must be finished before step E can begin.
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Step F must be finished before step E can begin.
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Visually, these requirements look like this:
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-->A--->B--
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/ \ \
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C -->D----->E
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\ /
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---->F-----
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Your first goal is to determine the order in which the steps should be
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completed. If more than one step is ready, choose the step which is first
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alphabetically. In this example, the steps would be completed as follows:
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• Only C is available, and so it is done first.
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• Next, both A and F are available. A is first alphabetically, so it is
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done next.
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• Then, even though F was available earlier, steps B and D are now also
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available, and B is the first alphabetically of the three.
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• After that, only D and F are available. E is not available because only
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some of its prerequisites are complete. Therefore, D is completed next.
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• F is the only choice, so it is done next.
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• Finally, E is completed.
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So, in this example, the correct order is CABDFE.
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In what order should the steps in your instructions be completed?
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Your puzzle answer was GKRVWBESYAMZDPTIUCFXQJLHNO.
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--- Part Two ---
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As you're about to begin construction, four of the Elves offer to help. "The
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sun will set soon; it'll go faster if we work together." Now, you need to
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account for multiple people working on steps simultaneously. If multiple
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steps are available, workers should still begin them in alphabetical order.
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Each step takes 60 seconds plus an amount corresponding to its letter: A=1,
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B=2, C=3, and so on. So, step A takes 60+1=61 seconds, while step Z takes
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60+26=86 seconds. No time is required between steps.
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To simplify things for the example, however, suppose you only have help from
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one Elf (a total of two workers) and that each step takes 60 fewer seconds
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(so that step A takes 1 second and step Z takes 26 seconds). Then, using the
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same instructions as above, this is how each second would be spent:
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Second Worker 1 Worker 2 Done
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0 C .
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1 C .
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2 C .
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3 A F C
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4 B F CA
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5 B F CA
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6 D F CAB
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7 D F CAB
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8 D F CAB
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9 D . CABF
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10 E . CABFD
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11 E . CABFD
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12 E . CABFD
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13 E . CABFD
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14 E . CABFD
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15 . . CABFDE
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Each row represents one second of time. The Second column identifies how
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many seconds have passed as of the beginning of that second. Each worker
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column shows the step that worker is currently doing (or . if they are
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idle). The Done column shows completed steps.
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Note that the order of the steps has changed; this is because steps now take
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time to finish and multiple workers can begin multiple steps simultaneously.
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In this example, it would take 15 seconds for two workers to complete these
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steps.
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With 5 workers and the 60+ second step durations described above, how long
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will it take to complete all of the steps?
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Your puzzle answer was 903.
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Both parts of this puzzle are complete! They provide two gold stars: **
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2018/about
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. https://adventofcode.com/2018/events
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. https://adventofcode.com/2018/settings
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. https://adventofcode.com/2018/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2018/support
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. https://adventofcode.com/2018
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. https://adventofcode.com/2018
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. https://adventofcode.com/2018/support
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. https://adventofcode.com/2018/sponsors
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. https://adventofcode.com/2018/leaderboard
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. https://adventofcode.com/2018/stats
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. https://adventofcode.com/2018/sponsors
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. https://adventofcode.com/2015/day/6
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. https://adventofcode.com/2018
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. https://adventofcode.com/2018/day/7/input
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