Coverage Summary for Class: Hailstone (day24p1)

 package day24p1
 
 import org.apache.commons.geometry.euclidean.twod.Vector2D
 
 fun List<Hailstone>.findNumberOfInteractions(testRange: ClosedFloatingPointRange<Double>): Long {
   var count = 0L
   for (i in 0 until size - 1) {
     for (j in i + 1 until size) {
       val intersection = this[i].intersection(this[j], testRange)
       if (intersection != null) {
         count++
       }
     }
   }
   return count
 }
 
 fun String.toHailstones(): List<Hailstone> = lineSequence().map { it.toHailstone() }.toList()
 
 fun String.toHailstone(): Hailstone {
   val nums = split(',', '@').map { it.trim().toLong() }
   return Hailstone(nums[0], nums[1], nums[2], nums[3], nums[4], nums[5])
 }
 
 data class Hailstone(val px: Long, val py: Long, val pz: Long, val vx: Long, val vy: Long, val vz: Long) {
 
   fun intersection(o: Hailstone): Vector2D? {
     val area = vx.toDouble() * o.vy - vy * o.vx
     if (area == 0.0) return null
 
     val t1 = ((py - o.py) * o.vx - (px - o.px) * o.vy) / area
 
     val t2 = (px - o.px + t1 * vx) / o.vx
 
     if (t1 < 0 || t2 < 0) return null
 
     return Vector2D.of(px + t1 * vx, py + t1 * vy)
   }
 
   fun intersection(other: Hailstone, testRange: ClosedFloatingPointRange<Double>): Vector2D? =
     intersection(other)?.let {
       if (it.x in testRange && it.y in testRange) it
       else null
     }
 }