110 lines
4.6 KiB
Plaintext
110 lines
4.6 KiB
Plaintext
Advent of Code
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--- Day 1: Chronal Calibration ---
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"We've detected some temporal anomalies," one of Santa's Elves at the
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Temporal Anomaly Research and Detection Instrument Station tells you. She
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sounded pretty worried when she called you down here. "At 500-year intervals
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into the past, someone has been changing Santa's history!"
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"The good news is that the changes won't propagate to our time stream for
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another 25 days, and we have a device" - she attaches something to your
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wrist - "that will let you fix the changes with no such propagation delay.
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It's configured to send you 500 years further into the past every few days;
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that was the best we could do on such short notice."
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"The bad news is that we are detecting roughly fifty anomalies throughout
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time; the device will indicate fixed anomalies with stars. The other bad
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news is that we only have one device and you're the best person for the job!
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Good lu--" She taps a button on the device and you suddenly feel like you're
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falling. To save Christmas, you need to get all fifty stars by December
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25th.
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Collect stars by solving puzzles. Two puzzles will be made available on each
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day in the advent calendar; the second puzzle is unlocked when you complete
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the first. Each puzzle grants one star. Good luck!
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After feeling like you've been falling for a few minutes, you look at the
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device's tiny screen. "Error: Device must be calibrated before first use.
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Frequency drift detected. Cannot maintain destination lock." Below the
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message, the device shows a sequence of changes in frequency (your puzzle
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input). A value like +6 means the current frequency increases by 6; a value
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like -3 means the current frequency decreases by 3.
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For example, if the device displays frequency changes of +1, -2, +3, +1,
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then starting from a frequency of zero, the following changes would occur:
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• Current frequency 0, change of +1; resulting frequency 1.
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• Current frequency 1, change of -2; resulting frequency -1.
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• Current frequency -1, change of +3; resulting frequency 2.
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• Current frequency 2, change of +1; resulting frequency 3.
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In this example, the resulting frequency is 3.
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Here are other example situations:
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• +1, +1, +1 results in 3
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• +1, +1, -2 results in 0
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• -1, -2, -3 results in -6
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Starting with a frequency of zero, what is the resulting frequency after all
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of the changes in frequency have been applied?
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Your puzzle answer was 553.
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--- Part Two ---
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You notice that the device repeats the same frequency change list over and
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over. To calibrate the device, you need to find the first frequency it
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reaches twice.
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For example, using the same list of changes above, the device would loop as
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follows:
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• Current frequency 0, change of +1; resulting frequency 1.
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• Current frequency 1, change of -2; resulting frequency -1.
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• Current frequency -1, change of +3; resulting frequency 2.
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• Current frequency 2, change of +1; resulting frequency 3.
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• (At this point, the device continues from the start of the list.)
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• Current frequency 3, change of +1; resulting frequency 4.
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• Current frequency 4, change of -2; resulting frequency 2, which has
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already been seen.
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In this example, the first frequency reached twice is 2. Note that your
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device might need to repeat its list of frequency changes many times before
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a duplicate frequency is found, and that duplicates might be found while in
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the middle of processing the list.
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Here are other examples:
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• +1, -1 first reaches 0 twice.
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• +3, +3, +4, -2, -4 first reaches 10 twice.
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• -6, +3, +8, +5, -6 first reaches 5 twice.
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• +7, +7, -2, -7, -4 first reaches 14 twice.
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What is the first frequency your device reaches twice?
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Your puzzle answer was 78724.
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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/2018
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. https://adventofcode.com/2018/day/1/input
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