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54 lines
1.7 KiB
Markdown
54 lines
1.7 KiB
Markdown
https://adventofcode.com/2023/day/3
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## \--- Day 3: Gear Ratios ---
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You and the Elf eventually reach a [gondola
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lift](https://en.wikipedia.org/wiki/Gondola_lift) station; he says the gondola
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lift will take you up to the _water source_ , but this is as far as he can
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bring you. You go inside.
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It doesn't take long to find the gondolas, but there seems to be a problem:
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they're not moving.
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"Aaah!"
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You turn around to see a slightly-greasy Elf with a wrench and a look of
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surprise. "Sorry, I wasn't expecting anyone! The gondola lift isn't working
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right now; it'll still be a while before I can fix it." You offer to help.
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The engineer explains that an engine part seems to be missing from the engine,
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but nobody can figure out which one. If you can _add up all the part numbers_
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in the engine schematic, it should be easy to work out which part is missing.
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The engine schematic (your puzzle input) consists of a visual representation
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of the engine. There are lots of numbers and symbols you don't really
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understand, but apparently _any number adjacent to a symbol_ , even
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diagonally, is a "part number" and should be included in your sum. (Periods
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(`.`) do not count as a symbol.)
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Here is an example engine schematic:
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[code]
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467..114..
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...*......
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..35..633.
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......#...
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617*......
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.....+.58.
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..592.....
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......755.
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...$.*....
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.664.598..
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[/code]
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In this schematic, two numbers are _not_ part numbers because they are not
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adjacent to a symbol: `114` (top right) and `58` (middle right). Every other
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number is adjacent to a symbol and so _is_ a part number; their sum is
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`_4361_`.
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Of course, the actual engine schematic is much larger. _What is the sum of all
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of the part numbers in the engine schematic?_
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