Merge with master.

Author: lakiboy

src/main/kotlin/io/dmitrijs/aoc2022/Day23.kt

@@ -21,7 +21,7 @@ class Day23(input: List<String>) {
  }
 
  private class Grid(input: List<Point>) {
- private var elves = input.toSet()
+ private val elves = input.toMutableSet()
  private var sides = Direction.values().toList()
 
  val emptyTiles get(): Int {
@@ -49,9 +49,15 @@ class Day23(input: List<String>) {
  val old = moving.values.toSet()
  val new = moving.keys
 
- elves = elves - old + new
+ elves.apply {
+ removeAll(old)
+ addAll(new)
+ }
  sides = sides.drop(1) + sides.first()
 
+ // Alternatively can be immutable, but mutable structure is faster.
+ // elves = elves - old + new
+
  return new.size
  }