172 lines
7.0 KiB
Plaintext
172 lines
7.0 KiB
Plaintext
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Advent of Code
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• [About]
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• [Events]
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• [Shop]
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• [Settings]
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• [Log Out]
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br0xen (AoC++) 28*
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<y>2022</y>
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• [Calendar]
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• [AoC++]
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• [Sponsors]
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• [Leaderboard]
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• [Stats]
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Our sponsors help make Advent of Code possible:
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BJSS - Our people are a team of problem solvers, experienced in evolving technologies and delivering
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world-class technology solutions.
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--- Day 15: Beacon Exclusion Zone ---
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You feel the ground rumble again as the distress signal leads you to a large network of subterranean tunnels.
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You don't have time to search them all, but you don't need to: your pack contains a set of deployable sensors
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that you imagine were originally built to locate lost Elves.
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The sensors aren't very powerful, but that's okay; your handheld device indicates that you're close enough to
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the source of the distress signal to use them. You pull the emergency sensor system out of your pack, hit the
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big button on top, and the sensors zoom off down the tunnels.
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Once a sensor finds a spot it thinks will give it a good reading, it attaches itself to a hard surface and
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begins monitoring for the nearest signal source beacon. Sensors and beacons always exist at integer
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coordinates. Each sensor knows its own position and can determine the position of a beacon precisely; however,
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sensors can only lock on to the one beacon closest to the sensor as measured by the Manhattan distance. (There
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is never a tie where two beacons are the same distance to a sensor.)
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It doesn't take long for the sensors to report back their positions and closest beacons (your puzzle input).
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For example:
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Sensor at x=2, y=18: closest beacon is at x=-2, y=15
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Sensor at x=9, y=16: closest beacon is at x=10, y=16
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Sensor at x=13, y=2: closest beacon is at x=15, y=3
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Sensor at x=12, y=14: closest beacon is at x=10, y=16
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Sensor at x=10, y=20: closest beacon is at x=10, y=16
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Sensor at x=14, y=17: closest beacon is at x=10, y=16
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Sensor at x=8, y=7: closest beacon is at x=2, y=10
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Sensor at x=2, y=0: closest beacon is at x=2, y=10
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Sensor at x=0, y=11: closest beacon is at x=2, y=10
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Sensor at x=20, y=14: closest beacon is at x=25, y=17
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Sensor at x=17, y=20: closest beacon is at x=21, y=22
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Sensor at x=16, y=7: closest beacon is at x=15, y=3
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Sensor at x=14, y=3: closest beacon is at x=15, y=3
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Sensor at x=20, y=1: closest beacon is at x=15, y=3
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So, consider the sensor at 2,18; the closest beacon to it is at -2,15. For the sensor at 9,16, the closest
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beacon to it is at 10,16.
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Drawing sensors as S and beacons as B, the above arrangement of sensors and beacons looks like this:
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1 1 2 2
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0 5 0 5 0 5
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0 ....S.......................
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1 ......................S.....
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2 ...............S............
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3 ................SB..........
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4 ............................
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5 ............................
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6 ............................
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7 ..........S.......S.........
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8 ............................
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9 ............................
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10 ....B.......................
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11 ..S.........................
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12 ............................
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13 ............................
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14 ..............S.......S.....
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15 B...........................
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16 ...........SB...............
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17 ................S..........B
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18 ....S.......................
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19 ............................
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20 ............S......S........
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21 ............................
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22 .......................B....
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This isn't necessarily a comprehensive map of all beacons in the area, though. Because each sensor only
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identifies its closest beacon, if a sensor detects a beacon, you know there are no other beacons that close or
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closer to that sensor. There could still be beacons that just happen to not be the closest beacon to any
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sensor. Consider the sensor at 8,7:
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1 1 2 2
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0 5 0 5 0 5
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-2 ..........#.................
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-1 .........###................
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0 ....S...#####...............
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1 .......#######........S.....
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2 ......#########S............
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3 .....###########SB..........
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4 ....#############...........
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5 ...###############..........
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6 ..#################.........
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7 .#########S#######S#........
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8 ..#################.........
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9 ...###############..........
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10 ....B############...........
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11 ..S..###########............
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12 ......#########.............
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13 .......#######..............
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14 ........#####.S.......S.....
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15 B........###................
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16 ..........#SB...............
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17 ................S..........B
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18 ....S.......................
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19 ............................
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20 ............S......S........
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21 ............................
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22 .......................B....
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This sensor's closest beacon is at 2,10, and so you know there are no beacons that close or closer (in any
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positions marked #).
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None of the detected beacons seem to be producing the distress signal, so you'll need to work out where the
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distress beacon is by working out where it isn't. For now, keep things simple by counting the positions where a
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beacon cannot possibly be along just a single row.
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So, suppose you have an arrangement of beacons and sensors like in the example above and, just in the row where
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y=10, you'd like to count the number of positions a beacon cannot possibly exist. The coverage from all sensors
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near that row looks like this:
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1 1 2 2
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0 5 0 5 0 5
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9 ...#########################...
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10 ..####B######################..
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11 .###S#############.###########.
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In this example, in the row where y=10, there are 26 positions where a beacon cannot be present.
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Consult the report from the sensors you just deployed. In the row where y=2000000, how many positions cannot
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contain a beacon?
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To begin, get your puzzle input.
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Answer: _____________________ [ [Submit] ]
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You can also [Shareon Twitter Mastodon] this puzzle.
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2022/about
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. https://adventofcode.com/2022/events
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. https://teespring.com/stores/advent-of-code
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. https://adventofcode.com/2022/settings
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. https://adventofcode.com/2022/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2022/support
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. https://adventofcode.com/2022
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. https://adventofcode.com/2022
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. https://adventofcode.com/2022/support
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. https://adventofcode.com/2022/sponsors
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. https://adventofcode.com/2022/leaderboard
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. https://adventofcode.com/2022/stats
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. https://adventofcode.com/2022/sponsors
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. https://www.bjss.com/
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. https://en.wikipedia.org/wiki/Taxicab_geometry
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. https://adventofcode.com/2022/day/15/input
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. https://twitter.com/intent/tweet?text=%22Beacon+Exclusion+Zone%22+%2D+Day+15+%2D+Advent+of+Code+2022&url=https%3A%2F%2Fadventofcode%2Ecom%2F2022%2Fday%2F15&related=ericwastl&hashtags=AdventOfCode
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. javascript:void(0);
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