66 lines
3.3 KiB
Markdown
66 lines
3.3 KiB
Markdown
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# 2021 Day 02: Dive!
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Copyright (c) Eric Wastl
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#### [Direct Link](https://adventofcode.com/2021/day/02)
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## Part 1
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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`, `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**, 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 should probably figure out where it's going. For example:
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```
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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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```
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Your horizontal position and depth both start at `0`. The steps above would 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 `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 planned course. `What do you get if you multiply your final horizontal position by your final depth?`
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## Part 2
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Based on your calculations, the planned course doesn't seem to make any sense. You find the submarine manual and discover that the process is actually slightly more complicated.
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In addition to horizontal position and depth, you'll also need to track a third value, **aim**, which also starts at `0`. The commands also mean 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 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 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 position and depth you would have after following the planned course. **What do you get if you multiply your final horizontal position by your final depth?**
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