91 lines
2.8 KiB
Org Mode
91 lines
2.8 KiB
Org Mode
** --- Day 4: Camp Cleanup ---
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Space needs to be cleared before the last supplies can be unloaded from
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the ships, and so several Elves have been assigned the job of cleaning
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up sections of the camp. Every section has a unique /ID number/, and
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each Elf is assigned a range of section IDs.
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However, as some of the Elves compare their section assignments with
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each other, they've noticed that many of the assignments /overlap/. To
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try to quickly find overlaps and reduce duplicated effort, the Elves
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pair up and make a /big list of the section assignments for each pair/
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(your puzzle input).
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For example, consider the following list of section assignment pairs:
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#+begin_example
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2-4,6-8
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2-3,4-5
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5-7,7-9
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2-8,3-7
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6-6,4-6
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2-6,4-8
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#+end_example
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For the first few pairs, this list means:
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- Within the first pair of Elves, the first Elf was assigned sections
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=2-4= (sections =2=, =3=, and =4=), while the second Elf was assigned
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sections =6-8= (sections =6=, =7=, =8=).
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- The Elves in the second pair were each assigned two sections.
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- The Elves in the third pair were each assigned three sections: one got
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sections =5=, =6=, and =7=, while the other also got =7=, plus =8= and
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=9=.
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This example list uses single-digit section IDs to make it easier to
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draw; your actual list might contain larger numbers. Visually, these
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pairs of section assignments look like this:
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#+begin_example
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.234..... 2-4
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.....678. 6-8
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.23...... 2-3
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...45.... 4-5
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....567.. 5-7
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......789 7-9
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.2345678. 2-8
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..34567.. 3-7
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.....6... 6-6
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...456... 4-6
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.23456... 2-6
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...45678. 4-8
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#+end_example
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Some of the pairs have noticed that one of their assignments /fully
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contains/ the other. For example, =2-8= fully contains =3-7=, and =6-6=
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is fully contained by =4-6=. In pairs where one assignment fully
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contains the other, one Elf in the pair would be exclusively cleaning
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sections their partner will already be cleaning, so these seem like the
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most in need of reconsideration. In this example, there are =2= such
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pairs.
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/In how many assignment pairs does one range fully contain the other?/
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Your puzzle answer was =444=.
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The first half of this puzzle is complete! It provides one gold star: *
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** --- Part Two ---
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It seems like there is still quite a bit of duplicate work planned.
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Instead, the Elves would like to know the number of pairs that /overlap
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at all/.
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In the above example, the first two pairs (=2-4,6-8= and =2-3,4-5=)
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don't overlap, while the remaining four pairs (=5-7,7-9=, =2-8,3-7=,
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=6-6,4-6=, and =2-6,4-8=) do overlap:
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- =5-7,7-9= overlaps in a single section, =7=.
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- =2-8,3-7= overlaps all of the sections =3= through =7=.
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- =6-6,4-6= overlaps in a single section, =6=.
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- =2-6,4-8= overlaps in sections =4=, =5=, and =6=.
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So, in this example, the number of overlapping assignment pairs is =4=.
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/In how many assignment pairs do the ranges overlap?/
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Answer:
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