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Day 09 simpler

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Paul-Henri Froidmont 2023-12-09 15:36:34 +01:00
parent e1a8169fd2
commit 97e472a693
Signed by: phfroidmont
GPG key ID: BE948AFD7E7873BE
1 changed files with 9 additions and 14 deletions
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21
src/day09.scala
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@ -11,25 +11,20 @@ val dayNumber = "09"
@main def part2: Unit = @main def part2: Unit =
println(part2(loadInput(dayNumber))) println(part2(loadInput(dayNumber)))
@tailrec def generateDifferences(acc: Array[Array[Long]]): Array[Array[Long]] = def findNextValue(history: Array[Long]): Long =
if acc.last.forall(_ == 0) then acc @tailrec def aux(history: Array[Long], acc: Long): Long =
if history.forall(_ == 0) then acc
else else
generateDifferences( aux(
acc.appended( history.sliding(2).map { case Array(l, r) => r - l }.toArray,
acc.last.sliding(2).map { case Array(l, r) => r - l }.toArray acc + history.last
)
) )
aux(history, 0)
def part1(input: String): String = def part1(input: String): String =
val readings = input.split('\n').map(_.split(' ').map(_.toLong)) val readings = input.split('\n').map(_.split(' ').map(_.toLong))
def findNextValue(history: Array[Long]): Long =
generateDifferences(Array(history)).map(_.last).sum
readings.map(findNextValue).sum.toString readings.map(findNextValue).sum.toString
def part2(input: String): String = def part2(input: String): String =
val readings = input.split('\n').map(_.split(' ').map(_.toLong)) val readings = input.split('\n').map(_.split(' ').map(_.toLong))
def findPreviousValue(history: Array[Long]): Long = readings.map(_.reverse).map(findNextValue).sum.toString
generateDifferences(Array(history))
.map(_.head)
.reduceRight((v, acc) => v - acc)
readings.map(findPreviousValue).sum.toString