95 lines
3.6 KiB
Plaintext
95 lines
3.6 KiB
Plaintext
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Advent of Code
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br0xen (AoC++) 4*
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--- Day 2: Red-Nosed Reports ---
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Fortunately, the first location The Historians want to search isn't a long
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walk from the Chief Historian's office.
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While the Red-Nosed Reindeer nuclear fusion/fission plant appears to
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contain no sign of the Chief Historian, the engineers there run up to you
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as soon as they see you. Apparently, they still talk about the time
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Rudolph was saved through molecular synthesis from a single electron.
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They're quick to add that - since you're already here - they'd really
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appreciate your help analyzing some unusual data from the Red-Nosed
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reactor. You turn to check if The Historians are waiting for you, but they
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seem to have already divided into groups that are currently searching
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every corner of the facility. You offer to help with the unusual data.
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The unusual data (your puzzle input) consists of many reports, one report
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per line. Each report is a list of numbers called levels that are
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separated by spaces. For example:
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7 6 4 2 1
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1 2 7 8 9
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9 7 6 2 1
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1 3 2 4 5
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8 6 4 4 1
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1 3 6 7 9
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This example data contains six reports each containing five levels.
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The engineers are trying to figure out which reports are safe. The
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Red-Nosed reactor safety systems can only tolerate levels that are either
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gradually increasing or gradually decreasing. So, a report only counts as
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safe if both of the following are true:
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• The levels are either all increasing or all decreasing.
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• Any two adjacent levels differ by at least one and at most three.
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In the example above, the reports can be found safe or unsafe by checking
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those rules:
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• 7 6 4 2 1: Safe because the levels are all decreasing by 1 or 2.
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• 1 2 7 8 9: Unsafe because 2 7 is an increase of 5.
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• 9 7 6 2 1: Unsafe because 6 2 is a decrease of 4.
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• 1 3 2 4 5: Unsafe because 1 3 is increasing but 3 2 is decreasing.
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• 8 6 4 4 1: Unsafe because 4 4 is neither an increase or a decrease.
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• 1 3 6 7 9: Safe because the levels are all increasing by 1, 2, or 3.
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So, in this example, 2 reports are safe.
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Analyze the unusual data from the engineers. How many reports are safe?
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Your puzzle answer was 479.
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--- Part Two ---
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The engineers are surprised by the low number of safe reports until they
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realize they forgot to tell you about the Problem Dampener.
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The Problem Dampener is a reactor-mounted module that lets the reactor
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safety systems tolerate a single bad level in what would otherwise be a
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safe report. It's like the bad level never happened!
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Now, the same rules apply as before, except if removing a single level
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from an unsafe report would make it safe, the report instead counts as
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safe.
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More of the above example's reports are now safe:
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• 7 6 4 2 1: Safe without removing any level.
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• 1 2 7 8 9: Unsafe regardless of which level is removed.
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• 9 7 6 2 1: Unsafe regardless of which level is removed.
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• 1 3 2 4 5: Safe by removing the second level, 3.
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• 8 6 4 4 1: Safe by removing the third level, 4.
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• 1 3 6 7 9: Safe without removing any level.
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Thanks to the Problem Dampener, 4 reports are actually safe!
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Update your analysis by handling situations where the Problem Dampener can
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remove a single level from unsafe reports. How many reports are now safe?
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Your puzzle answer was 531.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try
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another puzzle.
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If you still want to see it, you can get your puzzle input.
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References
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