77 lines
2.5 KiB
Scala
77 lines
2.5 KiB
Scala
|
package day10
|
||
|
|
||
|
import scala.collection.mutable
|
||
|
import scala.collection.mutable.ListBuffer
|
||
|
|
||
|
class Day10(input: List[List[Char]])
|
||
|
{
|
||
|
// Set of all asteroids represented by vectors from (0, 0)
|
||
|
val set: mutable.HashSet[Vector2] = new mutable.HashSet[Vector2]
|
||
|
|
||
|
// Parse input into the set
|
||
|
for (y <- input.indices; x <- input(0).indices) {
|
||
|
val char = input(y)(x)
|
||
|
if (char == '#') set.add(Vector2(x, y))
|
||
|
}
|
||
|
|
||
|
/** Solve part 1 */
|
||
|
def solveP1(): (Vector2, Int) =
|
||
|
{
|
||
|
// map each asteroid to number of other asteroid it can "see"
|
||
|
val map = new mutable.HashMap[Vector2, Int]
|
||
|
set.foreach(x => map.addOne(x, x.raycastSet(set).size))
|
||
|
map.toList.maxBy(_._2) // find the one with the most seen
|
||
|
}
|
||
|
|
||
|
def solveP2(): Vector2 =
|
||
|
{
|
||
|
//val center = solveP1()._1 // center
|
||
|
val center = Vector2(29,28) // when you assume you already know the answer
|
||
|
|
||
|
// Map angle to *queue* of points (multiple points can have same angle)
|
||
|
val angleMap = new mutable.HashMap[Vector2, ListBuffer[Vector2]]
|
||
|
|
||
|
// Write to the queues
|
||
|
set.foreach(x => {
|
||
|
val v2FromCenter = center.raycast(x)
|
||
|
if (angleMap.contains(v2FromCenter)) {
|
||
|
angleMap(v2FromCenter).addOne(center.toVector(x)) // Append to the end
|
||
|
}
|
||
|
else { // Doesn't exist -> add entry
|
||
|
angleMap.addOne(v2FromCenter, ListBuffer(center.toVector(x)))
|
||
|
}
|
||
|
})
|
||
|
angleMap.remove(Vector2(0,0)) // this is the center, we don't need it
|
||
|
angleMap.foreachEntry((_, b) => b.sortWith(_.distance < _.distance)) // Sort queues by distance
|
||
|
|
||
|
// get list of angles sorted from Y axis
|
||
|
def rayOrder():List[Vector2] = angleMap.keys.toList.sortWith(_.angleFromY < _.angleFromY)
|
||
|
|
||
|
// Find n-th deletion
|
||
|
def findNthDeletion(n: Int): Vector2 = {
|
||
|
var removals = 0
|
||
|
var lookedFor = Vector2(0,0)
|
||
|
|
||
|
def cyclicDelete(): Unit = {
|
||
|
val steps = rayOrder()
|
||
|
for(i <- steps.indices) {
|
||
|
removals += 1
|
||
|
val buffer = angleMap(steps(i))
|
||
|
val removedP = buffer.remove(0) // remove from queue the closest asteroid
|
||
|
if (removals == n) lookedFor = removedP // this is the one were looking for
|
||
|
if (buffer.isEmpty) // if queue is empty -> no more asteroids sharing a normal vector; remove key
|
||
|
{
|
||
|
angleMap.remove(steps(i))
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
while (angleMap.nonEmpty && removals < n) {
|
||
|
cyclicDelete()
|
||
|
}
|
||
|
center + lookedFor
|
||
|
}
|
||
|
|
||
|
findNthDeletion(200)
|
||
|
}
|
||
|
}
|