Day 9

src/main/kotlin/com/basdado/adventofcode/Day9.kt

@@ -0,0 +1,119 @@
+package com.basdado.adventofcode
+
+fun main() {
+    val day = Day9()
+
+//    val testGame = Day9.Game(9, 25)
+//    testGame.play()
+//   // Correct last line: 0 16 8 17 4 18 19 2 24 20 25 10 21 5 22 11 1 12 6 13 3 14 7 15
+//    println(testGame.playerScores.joinToString())
+//
+    day.puzzle1()
+    // Puzzle 1 answer = 385820
+    day.puzzle2()
+}
+
+class Day9 {
+
+    fun puzzle1() {
+        val input = lines("/day/9/input.txt")
+            .findFirst()
+            .get()
+        val regex = Regex("([0-9]+) players; last marble is worth ([0-9]+) points")
+        val match = regex.matchEntire(input)!!
+        val playerCount = match.groupValues[1].toInt()
+        val marbleCount = match.groupValues[2].toInt()
+
+        val game = Game(playerCount, marbleCount)
+        game.play()
+        println(game.playerScores.max())
+    }
+
+    fun puzzle2() {
+        val input = lines("/day/9/input.txt")
+            .findFirst()
+            .get()
+        val regex = Regex("([0-9]+) players; last marble is worth ([0-9]+) points")
+        val match = regex.matchEntire(input)!!
+        val playerCount = match.groupValues[1].toInt()
+        val marbleCount = match.groupValues[2].toInt() * 100
+
+        val game = Game(playerCount, marbleCount)
+        game.play()
+        println(game.playerScores.max())
+
+    }
+
+    class Game(val playerCount: Int, val marbleCount: Int) {
+
+        val playerScores = LongArray(playerCount)
+        val marbleCircle = DoubleLinkedList(0)
+
+        fun play() {
+
+            var marble = 1
+            var current = marbleCircle.first
+            var currentPlayer = 0
+            while(marble <= marbleCount) {
+
+//                println("$currentPlayer   ${current.value}   $marbleCircle")
+
+                if (marble % 23 == 0) {
+
+                    playerScores[currentPlayer] = playerScores[currentPlayer] + marble
+
+
+                    val toRemove = current.previous.previous.previous.previous.previous.previous.previous
+                    val prev = toRemove.previous
+                    val next = toRemove.next
+                    prev.next = next
+                    next.previous = prev
+
+                    playerScores[currentPlayer] = playerScores[currentPlayer] + toRemove.value
+                    current = next
+
+                } else {
+
+                    val newNode = DoubleLinkedList.Node(marble)
+                    newNode.previous = current.next
+                    newNode.next = current.next.next
+
+                    newNode.previous.next = newNode
+                    newNode.next.previous = newNode
+
+                    current = newNode
+                }
+                currentPlayer = (currentPlayer + 1) % playerCount
+                marble++
+
+            }
+//            println("$currentPlayer   ${current.value}   $marbleCircle")
+        }
+    }
+
+    class DoubleLinkedList<T>(firstEntry: T) {
+
+        class Node<T>(val value: T) {
+            var next: Node<T> = this
+            var previous: Node<T> = this
+        }
+
+        var first: Node<T>
+
+        init {
+            first = Node(firstEntry)
+        }
+
+        override fun toString(): String {
+
+            var node = first
+            var res = StringBuilder()
+            do {
+                res.append(node.value).append(" ")
+                node = node.next
+            } while (node != first)
+            return res.toString()
+        }
+
+    }
+}

src/main/resources/day/9/input.txt

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+468 players; last marble is worth 71843 points