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