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48 lines
No EOL
2.5 KiB
Markdown
48 lines
No EOL
2.5 KiB
Markdown
# Day 3: Rucksack Reorganization
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One Elf has the important job of loading all the rucksacks with supplies for the jungle journey. Unfortunately, that
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Elf didn't quite follow the packing instructions, and so a few items now need to be rearranged.
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Each rucksack has two large **compartments**. All items of a given type are meant to go into exactly one of the two
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compartments. The Elf that did the packing failed to follow this rule for exactly one item type per rucksack.
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The Elves have made a list of all the items currently in each rucksack (your puzzle input), but they need your help
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finding the errors. Every item type is identified by a single lowercase or uppercase letter (that is, `a` and `A` refer to
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different types of items).
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The list of items for each rucksack is given as characters all on a single line. A given rucksack always has the same
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number of items in each of its two compartments, so the first half of the characters represent items in the first
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compartment, while the second half of the characters represent items in the second compartment.
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For example, suppose you have the following list of contents from six rucksacks:
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```
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vJrwpWtwJgWrhcsFMMfFFhFp
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jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
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PmmdzqPrVvPwwTWBwg
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wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
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ttgJtRGJQctTZtZT
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CrZsJsPPZsGzwwsLwLmpwMDw
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```
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- The first rucksack contains the items `vJrwpWtwJgWrhcsFMMfFFhFp`, which means its first compartment contains the items
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`vJrwpWtwJgWr`, while the second compartment contains the items `hcsFMMfFFhFp`. The only item type that appears in
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both
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compartments is lowercase **p**.
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- The second rucksack's compartments contain `jqHRNqRjqzjGDLGL` and `rsFMfFZSrLrFZsSL`. The only item type that appears
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in
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both compartments is uppercase **L**.
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- The third rucksack's compartments contain `PmmdzqPrV` and `vPwwTWBwg`; the only common item type is uppercase **P**.
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- The fourth rucksack's compartments only share item type **v**.
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- The fifth rucksack's compartments only share item type **t**.
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- The sixth rucksack's compartments only share item type **s**.
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To help prioritize item rearrangement, every item type can be converted to a **priority**:
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- Lowercase item types a through z have priorities 1 through 26.
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- Uppercase item types A through Z have priorities 27 through 52.
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In the above example, the priority of the item type that appears in both compartments of each rucksack is 16 (p), 38 (
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L), 42 (P), 22 (v), 20 (t), and 19 (s); the sum of these is `157`.
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Find the item type that appears in both compartments of each rucksack. **What is the sum of the priorities of those item
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types?** |