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83 lines
3.3 KiB
Markdown
83 lines
3.3 KiB
Markdown
3 years ago
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https://adventofcode.com/2021/day/2
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## \--- Day 2: Dive! ---
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Now, you need to figure out how to pilot this thing.
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It seems like the submarine can take a series of commands like `forward 1`,
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`down 2`, or `up 3`:
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* `forward X` increases the horizontal position by `X` units.
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* `down X` _increases_ the depth by `X` units.
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* `up X` _decreases_ the depth by `X` units.
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Note that since you're on a submarine, `down` and `up` affect your _depth_ ,
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and so they have the opposite result of what you might expect.
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The submarine seems to already have a planned course (your puzzle input). You
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should probably figure out where it's going. For example:
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[code]
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forward 5
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down 5
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forward 8
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up 3
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down 8
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forward 2
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[/code]
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Your horizontal position and depth both start at `0`. The steps above would
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then modify them as follows:
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* `forward 5` adds `5` to your horizontal position, a total of `5`.
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* `down 5` adds `5` to your depth, resulting in a value of `5`.
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* `forward 8` adds `8` to your horizontal position, a total of `13`.
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* `up 3` decreases your depth by `3`, resulting in a value of `2`.
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* `down 8` adds `8` to your depth, resulting in a value of `10`.
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* `forward 2` adds `2` to your horizontal position, a total of `15`.
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After following these instructions, you would have a horizontal position of
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`15` and a depth of `10`. (Multiplying these together produces `_150_`.)
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Calculate the horizontal position and depth you would have after following the
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planned course. _What do you get if you multiply your final horizontal
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position by your final depth?_
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## \--- Part Two ---
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Based on your calculations, the planned course doesn't seem to make any sense.
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You find the submarine manual and discover that the process is actually
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slightly more complicated.
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In addition to horizontal position and depth, you'll also need to track a
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third value, _aim_ , which also starts at `0`. The commands also mean
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something entirely different than you first thought:
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* `down X` _increases_ your aim by `X` units.
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* `up X` _decreases_ your aim by `X` units.
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* `forward X` does two things:
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* It increases your horizontal position by `X` units.
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* It increases your depth by your aim _multiplied by_ `X`.
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Again note that since you're on a submarine, `down` and `up` do the opposite
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of what you might expect: "down" means aiming in the positive direction.
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Now, the above example does something different:
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* `forward 5` adds `5` to your horizontal position, a total of `5`. Because your aim is `0`, your depth does not change.
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* `down 5` adds `5` to your aim, resulting in a value of `5`.
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* `forward 8` adds `8` to your horizontal position, a total of `13`. Because your aim is `5`, your depth increases by `8*5=40`.
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* `up 3` decreases your aim by `3`, resulting in a value of `2`.
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* `down 8` adds `8` to your aim, resulting in a value of `10`.
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* `forward 2` adds `2` to your horizontal position, a total of `15`. Because your aim is `10`, your depth increases by `2*10=20` to a total of `60`.
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After following these new instructions, you would have a horizontal position
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of `15` and a depth of `60`. (Multiplying these produces `_900_`.)
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Using this new interpretation of the commands, calculate the horizontal
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position and depth you would have after following the planned course. _What do
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you get if you multiply your final horizontal position by your final depth?_
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