day 9 puzzle 2

README.md

@@ -5,11 +5,11 @@ This repo contains my attempt at this year's Advent of Code (2023)
 I will try and do some problems (probably not all of them) in Scala
 
 ## Progress:
-#### Stars: 17 / 50
+#### Stars: 18 / 50
 |        Mon        |        Tue        |        Wed        |        Thu        |        Fri        |        Sat        |        Sun        |
 |:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|
 |                   |                   |                   |                   | 1<br>:star::star: | 2<br>:star::star: | 3<br>:star::star: |
-| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: | 7<br>:star::star: | 8<br>:star::star: |    9<br>:star:    |        10         |
+| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: | 7<br>:star::star: | 8<br>:star::star: | 9<br>:star::star: |        10         |
 |        11         |        12         |        13         |        14         |        15         |        16         |        17         |
 |        18         |        19         |        20         |        21         |        22         |        23         |        24         |
 |        25         |                   |                   |                   |                   |                   |                   |

src/day9/Puzzle1.scala

@@ -1,9 +1,6 @@
 package day9
 
-import scala.collection.mutable
 import scala.io.{BufferedSource, Source}
-import scala.util.matching.Regex
-import scala.util.matching.Regex.Match
 
 object Puzzle1 {
   var series: Array[Series] = Array.empty

src/day9/Puzzle2.scala

@@ -0,0 +1,38 @@
+package day9
+
+import scala.io.{BufferedSource, Source}
+
+object Puzzle2 {
+  var series: Array[Series] = Array.empty
+
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: Array[String] = source.getLines().toArray
+
+    series = new Array(lines.length)
+
+    for ((line: String, i: Int) <- lines.zipWithIndex) {
+      series(i) = new Series(line.split(" ").map(_.toInt))
+    }
+
+    source.close()
+  }
+
+  def solve(path: String): Int = {
+    loadInput(path)
+
+    var solution: Int = 0
+
+    for (s: Series <- series) {
+      s.computeDiffs()
+      solution += s.reverseExtrapolate()
+    }
+
+    return solution
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Int = solve("./res/day9/input1.txt")
+    println(solution)
+  }
+}

src/day9/Series.scala

@@ -27,4 +27,13 @@ class Series {
     }
     return values(0).last
   }
+
+  def reverseExtrapolate(): Int = {
+    val len: Int = values(0).length
+    values.last(values.last.length-1) = 0
+    for (i: Int <- values.length-2 to 0 by -1) {
+      values(i)(len-i-1) = values(i)(0) - values(i+1)(len-i-2)
+    }
+    return values(0).last
+  }
 }

tests/day9/Puzzle2Test.scala

@@ -0,0 +1,9 @@
+package day9
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Puzzle2Test extends AnyFunSuite {
+  test("Puzzle2.solve") {
+    assert(Puzzle2.solve("tests_res/day9/input1.txt") == 2)
+  }
+}