91 lines
2.8 KiB
Markdown
91 lines
2.8 KiB
Markdown
## \-\-- Day 24: Electromagnetic Moat \-\--
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The CPU itself is a large, black building surrounded by a bottomless
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pit. Enormous metal tubes extend outward from the side of the building
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at regular intervals and descend down into the void. There\'s no way to
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cross, but you need to get inside.
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No way, of course, other than building a *bridge* out of the magnetic
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components strewn about nearby.
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Each component has two *ports*, one on each end. The ports come in all
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different types, and only matching types can be connected. You take an
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inventory of the components by their port types (your puzzle input).
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Each port is identified by the number of *pins* it uses; more pins mean
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a stronger connection for your bridge. A `3/7` component, for example,
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has a type-`3` port on one side, and a type-`7` port on the other.
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Your side of the pit is metallic; a perfect surface to connect a
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magnetic, *zero-pin port*. Because of this, the first port you use must
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be of type `0`. It doesn\'t matter what type of port you end with; your
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goal is just to make the bridge as strong as possible.
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The *strength* of a bridge is the sum of the port types in each
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component. For example, if your bridge is made of components `0/3`,
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`3/7`, and `7/4`, your bridge has a strength of `0+3 + 3+7 + 7+4 = 24`.
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For example, suppose you had the following components:
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0/2
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2/2
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2/3
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3/4
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3/5
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0/1
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10/1
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9/10
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With them, you could make the following valid bridges:
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- `0/1`
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- `0/1`\--`10/1`
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- `0/1`\--`10/1`\--`9/10`
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- `0/2`
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- `0/2`\--`2/3`
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- `0/2`\--`2/3`\--`3/4`
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- `0/2`\--`2/3`\--`3/5`
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- `0/2`\--`2/2`
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- `0/2`\--`2/2`\--`2/3`
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- `0/2`\--`2/2`\--`2/3`\--`3/4`
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- `0/2`\--`2/2`\--`2/3`\--`3/5`
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(Note how, as shown by `10/1`, order of ports within a component
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doesn\'t matter. However, you may only use each port on a component
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once.)
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Of these bridges, the *strongest* one is `0/1`\--`10/1`\--`9/10`; it has
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a strength of `0+1 + 1+10 + 10+9 = 31`.
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*What is the strength of the strongest bridge you can make* with the
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components you have available?
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Your puzzle answer was `2006`.
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## \-\-- Part Two \-\-- {#part2}
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The bridge you\'ve built isn\'t long enough; you can\'t [jump the rest
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of the way]{title="Who do you think you are, Mario?"}.
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In the example above, there are two longest bridges:
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- `0/2`\--`2/2`\--`2/3`\--`3/4`
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- `0/2`\--`2/2`\--`2/3`\--`3/5`
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Of them, the one which uses the `3/5` component is stronger; its
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strength is `0+2 + 2+2 + 2+3 + 3+5 = 19`.
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*What is the strength of the longest bridge you can make?* If you can
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make multiple bridges of the longest length, pick the *strongest* one.
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Your puzzle answer was `1994`.
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Both parts of this puzzle are complete! They provide two gold stars:
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\*\*
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At this point, you should [return to your Advent calendar](/2017) and
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try another puzzle.
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If you still want to see it, you can [get your puzzle
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input](24/input).
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