feat(day18): part 1

Author: fdlk

build.sbt

@@ -25,7 +25,7 @@ version := "1.0"
 // Want to use a published library in your project?
 // You can define other libraries as dependencies in your build like this:
 
-libraryDependencies += "org.scala-lang.modules" %% "scala-parser-combinators" % "1.1.2"
+libraryDependencies += "com.lihaoyi" %% "fastparse" % "2.3.3"
 
 // Here, `libraryDependencies` is a set of dependencies, and by using `+=`,
 // we're adding the scala-parser-combinators dependency to the set of dependencies

day18.sc

@@ -0,0 +1,80 @@
+import common.loadPackets
+import fastparse.SingleLineWhitespace._
+import fastparse._
+
+import scala.annotation.tailrec
+import scala.util.matching.Regex
+
+val input = loadPackets(List("day18.txt"))
+
+@tailrec
+def findExplodeIndex(string: String, depth: Int = 0, index: Int = 0): Option[Int] =
+  string.headOption match {
+    case None => None
+    case Some('[') if depth == 4 => Some(index)
+    case Some('[') => findExplodeIndex(string.tail, depth + 1, index + 1)
+    case Some(']') => findExplodeIndex(string.tail, depth - 1, index + 1)
+    case _ => findExplodeIndex(string.tail, depth, index + 1)
+  }
+
+val pairRegex = """\[(\d+),(\d+)]""".r
+def parsePair(pair: String): (Int, Int) = pair match {
+  case pairRegex(left, right) => (left.toInt, right.toInt)
+}
+
+val digitsRegex = """\d+""".r
+
+def addToMatchIfPresent(string: String, toAdd: Int, m: Option[Regex.Match]): String =
+  m.map(m =>
+    List(string.substring(0, m.start),
+      m.toString.toInt + toAdd,
+      string.substring(m.end)).mkString)
+    .getOrElse(string)
+
+def addLeftIfPresent(string: String, toAdd: Int): String =
+  addToMatchIfPresent(string, toAdd, digitsRegex.findAllMatchIn(string).toList.lastOption)
+
+def addRightIfPresent(string: String, toAdd: Int): String =
+  addToMatchIfPresent(string, toAdd, digitsRegex.findFirstMatchIn(string))
+
+def explode(string: String): Option[String] =
+  findExplodeIndex(string).map(from => {
+    val to = string.indexOf(']', from) + 1
+    val (left, right) = parsePair(string.substring(from, to))
+    val before = string.substring(0, from)
+    val after = string.substring(to)
+    List(addLeftIfPresent(before, left), "0", addRightIfPresent(after, right)).mkString
+  })
+
+val splitRegex = """\d{2,}""".r
+def split(string: String): Option[String] =
+  splitRegex.findFirstMatchIn(string).map(m => {
+    val value = m.toString.toInt
+    val left = value / 2
+    val right = value - left
+    List(string.substring(0, m.start), s"[${left},${right}]", string.substring(m.end)).mkString
+  })
+
+@tailrec
+def reduce(string: String): String = {
+  explode(string).orElse(split(string)) match {
+    case Some(reduction) => reduce(reduction)
+    case None => string
+  }
+}
+
+def add(left: String, right: String): String =
+  reduce(s"[${left},${right}]")
+
+val reduced = input.reduce(add)
+
+object Parser {
+  def number[_: P]: P[Int] = CharIn("0-9").rep(1).!.map(_.toInt)
+  def expression[_: P]: P[Int] = P("[" ~ (number | expression) ~ "," ~ (number|expression) ~ "]").map{
+    case(left, right) => 3 * left + 2 * right
+  }
+  def magnitude(string: String): Parsed[Int] = parse(string, expression(_))
+}
+
+val part1 = Parser.magnitude(reduced)
+

src/main/resources/day18.txt

@@ -0,0 +1,100 @@
+[[[5,[4,8]],0],[[[2,2],5],[7,9]]]
+[[[[4,2],0],[4,[9,9]]],[[[7,0],[9,8]],5]]
+[[[[3,2],2],4],0]
+[[8,7],[[9,4],[8,[5,5]]]]
+[[[1,7],[[8,2],[3,5]]],[6,8]]
+[[[[7,1],[4,2]],[[6,0],[3,8]]],[[[5,2],8],[7,[4,7]]]]
+[[6,[5,8]],[[4,[3,0]],5]]
+[[[[1,2],[1,5]],[[7,1],6]],[2,[4,7]]]
+[[9,[[5,3],3]],9]
+[6,[[[6,1],2],[6,[5,6]]]]
+[[[9,8],[[5,6],7]],[[4,[9,9]],[8,1]]]
+[[4,7],[[[3,1],[1,5]],[5,8]]]
+[[[9,7],[5,[6,0]]],[[9,[3,5]],7]]
+[[[[1,2],[1,4]],4],0]
+[[[[0,0],[1,2]],[[0,2],[1,6]]],[0,[[6,2],[5,1]]]]
+[[[1,2],[[0,2],4]],[[5,[7,3]],2]]
+[[5,[1,[6,3]]],[5,[2,[5,3]]]]
+[[[9,[7,7]],7],[[8,1],[[9,1],7]]]
+[[[[6,5],6],[6,5]],[7,[9,[3,9]]]]
+[[6,[9,3]],6]
+[[5,[[2,3],[9,1]]],[0,[[5,8],4]]]
+[[[[4,9],[2,3]],7],6]
+[[[2,6],6],[[[9,0],9],[4,[6,1]]]]
+[[[9,[9,1]],[4,4]],[0,[6,8]]]
+[8,[2,[[0,4],[5,4]]]]
+[[3,[9,4]],[[0,[6,9]],2]]
+[[[1,1],[[0,1],[1,9]]],[[5,4],[6,9]]]
+[4,[2,[[6,9],0]]]
+[[[6,[3,7]],[3,7]],[1,[2,[4,7]]]]
+[[[[6,4],[0,0]],[[8,2],5]],[[8,[2,4]],[4,[9,1]]]]
+[[[[8,1],[8,0]],[5,[7,6]]],[2,[[0,2],[9,2]]]]
+[[6,7],[[9,[1,1]],[[9,2],9]]]
+[[[[7,2],[8,8]],0],4]
+[[[2,1],[[3,1],9]],9]
+[[[[5,5],9],[[7,8],[6,0]]],[[[4,0],[0,6]],[6,2]]]
+[[6,[3,[9,4]]],[[[5,5],5],2]]
+[[[4,3],[9,[8,4]]],4]
+[[[0,[5,9]],[[9,6],8]],[7,[3,[8,9]]]]
+[[6,[[8,2],[0,2]]],[[8,8],[[7,9],2]]]
+[[[0,[8,0]],7],[[[7,2],[6,6]],[[5,5],5]]]
+[5,[[1,[3,6]],[[0,7],6]]]
+[0,[[[5,7],[6,2]],8]]
+[[[4,[5,4]],[[2,9],[5,3]]],[7,[2,4]]]
+[[6,[[8,4],6]],9]
+[[[7,[7,7]],[2,9]],[8,[5,[6,4]]]]
+[[[[7,9],[9,9]],[[6,1],[5,5]]],[[[4,3],[7,3]],[6,[0,3]]]]
+[[2,[2,0]],6]
+[[[[2,3],2],1],[0,2]]
+[[[[8,6],[5,6]],3],1]
+[[[[4,9],[2,4]],2],[2,[[6,3],[3,4]]]]
+[0,[[[1,0],[4,0]],8]]
+[[4,[6,[2,1]]],[[[5,8],4],[[8,0],4]]]
+[[[0,0],[[3,4],1]],[9,[1,[7,0]]]]
+[[0,0],[[[9,3],8],[[1,7],[4,6]]]]
+[[[4,3],3],[[[3,3],9],9]]
+[[[[2,0],[0,1]],[[1,2],[1,0]]],[[[6,6],1],[7,1]]]
+[[1,[[2,7],9]],[[[9,1],6],[[7,0],0]]]
+[[7,[[5,4],0]],8]
+[[6,9],[[[8,1],6],[5,[1,2]]]]
+[[7,6],[[[1,9],2],[0,3]]]
+[[[9,7],[9,[5,2]]],[[[0,0],2],[0,8]]]
+[[9,[6,2]],[5,8]]
+[[[6,[0,3]],[[5,1],[4,4]]],[6,[5,[1,9]]]]
+[[8,8],[[[3,1],7],[[8,3],3]]]
+[[[[1,1],[9,5]],9],[[[2,8],[6,4]],[[1,2],[4,5]]]]
+[[[1,7],8],[[5,[0,6]],[9,[3,3]]]]
+[[7,3],[[[8,2],3],4]]
+[[9,3],[[1,[7,0]],5]]
+[[[9,[2,2]],[7,5]],[[7,[1,7]],[[0,5],7]]]
+[[1,[[0,3],3]],1]
+[[9,[[3,0],[9,0]]],1]
+[[2,[[3,9],7]],[[[8,1],[7,2]],[9,[6,3]]]]
+[4,[[0,[0,4]],[0,1]]]
+[[[[2,8],6],[[6,6],[5,8]]],[[1,[7,5]],[[2,2],[6,0]]]]
+[[[6,7],8],[[[1,5],[9,3]],[0,2]]]
+[[[[6,6],[6,2]],[0,6]],[[[1,5],2],[[0,3],[3,9]]]]
+[[5,[8,2]],[3,8]]
+[[8,7],[[0,5],[3,[6,8]]]]
+[[6,[[2,3],5]],[[9,[0,8]],[[2,4],[1,8]]]]
+[[[[5,7],[4,3]],[[5,4],5]],[0,[[6,5],2]]]
+[2,[[5,[0,7]],[3,[4,0]]]]
+[1,9]
+[[[[1,4],1],[0,[1,2]]],2]
+[[4,3],[5,[6,4]]]
+[[[4,4],[[8,0],[6,5]]],[[4,[9,1]],[[1,1],[2,2]]]]
+[[4,3],[[[1,1],1],[[4,6],[5,7]]]]
+[[[[6,1],[5,3]],2],[[[0,6],[7,3]],8]]
+[[[2,8],5],[1,[3,[8,7]]]]
+[[7,[5,[9,0]]],[[[9,1],2],[2,[9,6]]]]
+[[[[7,3],1],[[4,6],[5,1]]],[[[4,7],4],[[5,2],[3,7]]]]
+[[[[2,3],8],[7,8]],[[[5,5],[2,5]],[[6,8],1]]]
+[[[2,1],[[8,9],[4,3]]],[[8,[9,0]],7]]
+[[[[8,2],5],0],[[8,[9,6]],[[6,1],1]]]
+[[[3,[4,9]],[[5,4],[2,2]]],4]
+[[[[9,8],4],[[7,4],9]],[[0,7],6]]
+[[7,[[6,1],8]],[[2,0],[2,5]]]
+[[[[3,2],6],5],6]
+[6,[3,5]]
+[[[[7,1],7],4],[[[4,6],5],[1,[7,9]]]]
+[[[[7,0],7],[8,9]],[5,[[2,5],6]]]