Coverage Summary for Class: Network (day08p2)

 package day08p2
 
 import day08p2.Instruction.Left
 import day08p2.Instruction.Right
 import org.apache.commons.math3.util.ArithmeticUtils
 
 fun String.toInstructionListAndNetwork(): Pair<List<Instruction>, Network> {
   val lines = lineSequence()
   return lines.first().toInstructionList() to lines.drop(2).toNetwork()
 }
 
 fun Sequence<String>.toNetwork(): Network = Network(
   map { it.toNode() }.associateBy { it.id }
 )
 
 fun String.toNetwork(): Network = lineSequence().toNetwork()
 
 data class Network(val nodes: Map<NodeId, Node>) {
   fun calculateNumberOfSteps(instructions: List<Instruction>): Long =
     nodes.asSequence().filter { (id, _) -> id.starting }.map { (id, _) -> calculateNumberOfSteps(instructions, id) }
       .reduce(ArithmeticUtils::lcm)
 
   private fun calculateNumberOfSteps(instructions: List<Instruction>, start: NodeId): Long {
     var currentNode = nodes.getValue(start)
     var steps = 0
     while (true) {
       val nextId = currentNode.doStep(instructions[steps % instructions.size])
       currentNode = nodes.getValue(nextId)
       steps++
       if (nextId.ending) {
         return steps.toLong()
       }
     }
   }
 }
 
 enum class Instruction { Left, Right }
 
 fun String.toInstructionList(): List<Instruction> = this
   .map {
     when (it) {
       'L' -> Left
       else -> Right
     }
   }
   .toList()
 
 fun String.toNode(): Node {
   val (id, left, right) = """(.+) = \((.+), (.+)\)""".toRegex().matchEntire(this)?.destructured!!
   return Node(id = NodeId(id), left = NodeId(left), right = NodeId(right))
 }
 
 data class Node(val id: NodeId, val left: NodeId, val right: NodeId) {
   fun doStep(instruction: Instruction): NodeId = when (instruction) {
     Left -> left
     Right -> right
   }
 
   constructor(id: String, left: String, right: String) : this(NodeId(id), NodeId(left), NodeId(right))
 }
 
 data class NodeId(val value: String) {
   val starting: Boolean = value.last() == 'A'
   val ending: Boolean = value.last() == 'Z'
 }