77 lines
4.8 KiB
Text
77 lines
4.8 KiB
Text
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Your ferry made decent progress toward the island, but the storm came in faster than anyone expected. The ferry needs to take *evasive actions*!
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Unfortunately, the ship's navigation computer seems to be malfunctioning; rather than giving a route directly to safety, it produced extremely circuitous instructions. When the captain uses the [PA system](https://en.wikipedia.org/wiki/Public_address_system) to ask if anyone can help, you quickly volunteer.
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The navigation instructions (your puzzle input) consists of a sequence of single-character *actions* paired with integer input *values*. After staring at them for a few minutes, you work out what they probably mean:
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* Action *`N`* means to move *north* by the given value.
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* Action *`S`* means to move *south* by the given value.
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* Action *`E`* means to move *east* by the given value.
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* Action *`W`* means to move *west* by the given value.
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* Action *`L`* means to turn *left* the given number of degrees.
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* Action *`R`* means to turn *right* the given number of degrees.
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* Action *`F`* means to move *forward* by the given value in the direction the ship is currently facing.
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The ship starts by facing *east*. Only the `L` and `R` actions change the direction the ship is facing. (That is, if the ship is facing east and the next instruction is `N10`, the ship would move north 10 units, but would still move east if the following action were `F`.)
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For example:
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```
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F10
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N3
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F7
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R90
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F11
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```
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These instructions would be handled as follows:
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* `F10` would move the ship 10 units east (because the ship starts by facing east) to *east 10, north 0*.
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* `N3` would move the ship 3 units north to *east 10, north 3*.
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* `F7` would move the ship another 7 units east (because the ship is still facing east) to *east 17, north 3*.
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* `R90` would cause the ship to turn right by 90 degrees and face *south*; it remains at *east 17, north 3*.
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* `F11` would move the ship 11 units south to *east 17, south 8*.
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At the end of these instructions, the ship's [Manhattan distance](https://en.wikipedia.org/wiki/Manhattan_distance) (sum of the absolute values of its east/west position and its north/south position) from its starting position is `17 + 8` = *`25`*.
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Figure out where the navigation instructions lead. *What is the Manhattan distance between that location and the ship's starting position?*
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Your puzzle answer was `1032`.
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\--- Part Two ---
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----------
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Before you can give the destination to the captain, you realize that the actual action meanings were printed on the back of the instructions the whole time.
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Almost all of the actions indicate how to move a *waypoint* which is relative to the ship's position:
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* Action *`N`* means to move the waypoint *north* by the given value.
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* Action *`S`* means to move the waypoint *south* by the given value.
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* Action *`E`* means to move the waypoint *east* by the given value.
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* Action *`W`* means to move the waypoint *west* by the given value.
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* Action *`L`* means to rotate the waypoint around the ship *left* (*counter-clockwise*) the given number of degrees.
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* Action *`R`* means to rotate the waypoint around the ship *right* (*clockwise*) the given number of degrees.
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* Action *`F`* means to move *forward* to the waypoint a number of times equal to the given value.
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The waypoint starts *10 units east and 1 unit north* relative to the ship. The waypoint is relative to the ship; that is, if the ship moves, the waypoint moves with it.
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For example, using the same instructions as above:
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* `F10` moves the ship to the waypoint 10 times (a total of *100 units east and 10 units north*), leaving the ship at *east 100, north 10*. The waypoint stays 10 units east and 1 unit north of the ship.
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* `N3` moves the waypoint 3 units north to *10 units east and 4 units north of the ship*. The ship remains at *east 100, north 10*.
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* `F7` moves the ship to the waypoint 7 times (a total of *70 units east and 28 units north*), leaving the ship at *east 170, north 38*. The waypoint stays 10 units east and 4 units north of the ship.
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* `R90` rotates the waypoint around the ship clockwise 90 degrees, moving it to *4 units east and 10 units south of the ship*. The ship remains at *east 170, north 38*.
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* `F11` moves the ship to the waypoint 11 times (a total of *44 units east and 110 units south*), leaving the ship at *east 214, south 72*. The waypoint stays 4 units east and 10 units south of the ship.
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After these operations, the ship's Manhattan distance from its starting position is `214 + 72` = *`286`*.
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Figure out where the navigation instructions actually lead. *What is the Manhattan distance between that location and the ship's starting position?*
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Your puzzle answer was `156735`.
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Both parts of this puzzle are complete! They provide two gold stars: \*\*
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At this point, you should [return to your Advent calendar](/2020) and try another puzzle.
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If you still want to see it, you can [get your puzzle input](12/input).
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