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