Day9.scala

import scala.collection.mutable

object Day9 extends App {

  println("Hello Day9")

  val sampleArray: Array[Long] = Array(35, 20, 15, 25, 47, 40, 62, 55, 65, 95, 102, 117, 150, 182, 127, 219, 299, 277, 309, 576)

  val quizCalculator = { (preamble: Int, sampleArray: Array[Long]) =>
    val answer1 = findInvalidNumber(preamble, sampleArray)
    answer1.foreach(num => println(s"findInvalidNumber - the answer is ${num}"))

    val answer2 = answer1.flatMap {
      findEncryptionWeakness(_, sampleArray)
    }
    answer2.foreach(num => println(s"findEncryptionWeakness - the answer is ${num}"))
  }

  quizCalculator(5, sampleArray)
  quizCalculator(25, QuizSampleCode.getSampleCodeArray)

  def findInvalidNumber(preamble: Int, sampleArray: Array[Long]): Option[Long] = {
    var firstIndex = 0
    var lastIndex = preamble
    sampleArray.drop(preamble).foreach { number =>
      val set = mutable.HashSet[Long]().empty
      val slicedArray = sampleArray.slice(firstIndex, lastIndex).sorted
      val sumList = slicedArray.zipWithIndex.flatMap { n: (Long, Int) =>
        slicedArray.patch(n._2, Nil, 1).map(n._1 + _)
      }
      set ++= sumList
      if (!set.contains(number)) {
        return Some(number)
      }
      firstIndex += 1
      lastIndex += 1
    }
    None
  }

  def findEncryptionWeakness(invalidNumber: Long, sampleArray: Array[Long]): Option[Long] = {
    var leftIndex = 0
    var rightIndex = leftIndex + 1
    val filteredList = sampleArray.filter(_ <= invalidNumber)

    while (leftIndex < filteredList.size) {
      val slicedList = filteredList.slice(leftIndex, rightIndex + 1)
      val sum = slicedList.sum
      sum match {
        case s if s > invalidNumber => {
          leftIndex += 1
          rightIndex = +1
        }
        case s if s < invalidNumber => rightIndex += 1
        case s if s == invalidNumber => {
          return Some(slicedList.min + slicedList.max)
        }
      }
    }
    None
  }
}