feat(aoc-2023): day4 part 1 and 2

Author: markkovari

2023/src/main/scala/day04.scala

@@ -0,0 +1,84 @@
+package com.markkovari.adventofcode.day04
+
+import scala.util.matching.Regex.Match
+
+case class Card(id: Int, numbers: List[Int], winningNumbers: List[Int]) {
+  private def matches(): Set[Int] = {
+    numbers.toSet.intersect(winningNumbers.toSet)
+  }
+
+  def getScore(): Int = {
+    math.pow(2, matches().size - 1).intValue
+  }
+}
+
+def parseCard(input: String): Card =
+  input match {
+    case s"Card ${id}: ${numbers} | ${winningNumbers}" =>
+      Card(
+        id.trim().toInt,
+        // Sould be able to do this with a regex, but I can't figure it out right now :| by "whitespaces""
+        numbers.split(" ").filter(!_.isEmpty).map(_.toInt).toList,
+        winningNumbers.split(" ").filter(!_.isEmpty).map(_.toInt).toList
+      )
+  }
+
+def parseCards(input: String): List[Card] =
+  input.split("\n").map(parseCard).toList
+
+def part2(input: String): BigInt =
+  parseCards(input)
+    .map(_.getScore())
+    .foldLeft((0, Vector(1))) { case ((numCards, multiplicities), winning) =>
+      val thisMult = multiplicities(0)
+      val restMult = multiplicities
+        .drop(1)
+        .padTo(Math.max(1, winning), 1)
+        .zipWithIndex
+        .map((mult, idx) => if idx < winning then mult + thisMult else mult)
+      (numCards + thisMult, restMult)
+    }
+    ._1
+
+def countWinning(card: String): Int =
+  val numbers = card
+    .substring(card.indexOf(":") + 1) // discard "Card X:"
+    .split(" ")
+    .filterNot(_.isEmpty())
+  val (winningNumberStrs, givenNumberStrs) = numbers.span(_ != "|")
+  val winningNumbers = winningNumberStrs.map(_.toInt).toSet
+  // drop the initial "|"
+  val givenNumbers = givenNumberStrs.drop(1).map(_.toInt).toSet
+  winningNumbers.intersect(givenNumbers).size
+end countWinning
+
+def winningCounts(input: String): Iterator[Int] =
+  input.linesIterator.map(countWinning)
+end winningCounts
+
+def part1_(input: String): String =
+  winningCounts(input)
+    .map(winning => if winning > 0 then Math.pow(2, winning - 1).toInt else 0)
+    .sum
+    .toString()
+end part1_
+
+def part2_(input: String): String =
+  winningCounts(input)
+    // we only track the multiplicities of the next few cards as needed, not all of them;
+    // and the first element always exists, and corresponds to the current card;
+    // and the elements are always positive (because there is at least 1 original copy of each card)
+    .foldLeft((0, Vector(1))) { case ((numCards, multiplicities), winning) =>
+      val thisMult = multiplicities(0)
+      val restMult = multiplicities
+        .drop(1)
+        // these are the original copies of the next few cards
+        .padTo(Math.max(1, winning), 1)
+        .zipWithIndex
+        // these are the extra copies we just won
+        .map((mult, idx) => if idx < winning then mult + thisMult else mult)
+      (numCards + thisMult, restMult)
+    }
+    ._1
+    .toString()
+end part2_

2023/src/main/resources/1/example_1 2023/src/test/resources/1/example_12023/src/main/resources/1/example_1 renamed to 2023/src/test/resources/1/example_1

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+Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11