Part 1 solved, part 2 got issues.

day06.kts

@@ -0,0 +1,130 @@
+#!/usr/bin/env kotlin
+import java.io.File
+import java.lang.RuntimeException
+import java.util.Scanner
+
+data class MoveResult(val newLocation: Pair<Int, Int>, val newDirection: Direction)
+data class MoveHistory(val location: Pair<Int, Int>, val direction: Direction)
+enum class Direction(val offset: Pair<Int, Int>) {
+    NORTH(Pair(0, -1)),
+    EAST(Pair(1, 0)),
+    SOUTH(Pair(0, 1)),
+    WEST(Pair(-1, 0));
+
+    fun move(currentLocation: Pair<Int, Int>): Pair<Int, Int> {
+        return Pair(
+            currentLocation.first + offset.first,
+            currentLocation.second + offset.second
+        )
+    }
+    fun turnLeft(): Direction {
+        return when (this) {
+            NORTH -> WEST
+            WEST -> SOUTH
+            SOUTH -> EAST
+            EAST -> NORTH
+        }
+    }
+    fun turnRight(): Direction {
+        return when (this) {
+            NORTH -> EAST
+            EAST -> SOUTH
+            SOUTH -> WEST
+            WEST -> NORTH
+        }
+    }
+    fun moveByPartOneRules(
+        currentLocation: Pair<Int, Int>,
+        blocks: Set<Pair<Int, Int>>
+    ): MoveResult {
+        var currentDirection = this
+        do {
+            val potentialMove = currentDirection.move(currentLocation)
+            if (potentialMove !in blocks) {
+                return MoveResult(potentialMove, currentDirection)
+            }
+            currentDirection = currentDirection.turnRight()
+        } while (currentDirection != this)
+        throw RuntimeException("Nowhere to go! $currentLocation $this")
+    }
+}
+fun isPositionInTheRoom(player: Pair<Int, Int>, xMax: Int, yMax: Int): Boolean {
+    return player.first in 0..xMax && player.second in 0..yMax
+}
+
+
+val scanner = Scanner(System.`in`)
+val visited = mutableSetOf<Pair<Int, Int>>()
+val history = mutableListOf<MoveHistory>()
+var playerLocation = Pair(0, 0)
+var playerDirection: Direction = Direction.NORTH
+val blocks = mutableSetOf<Pair<Int, Int>>()
+val potentialBlocks = mutableSetOf<Pair<Int, Int>>()
+var yMax = 0
+var xMax = 0
+while (scanner.hasNextLine()) {
+    val line = scanner.nextLine()
+    for (i in line.indices) {
+        if (line[i] == '.') {
+            continue
+        }
+        if (line[i] == '>') {
+            playerDirection = Direction.EAST
+            playerLocation = Pair(i, yMax)
+        } else if (line[i] == '<') {
+            playerDirection = Direction.WEST
+            playerLocation = Pair(i, yMax)
+        } else if (line[i] == '^') {
+            playerDirection = Direction.NORTH
+            playerLocation = Pair(i, yMax)
+        } else if (line[i] == 'v') {
+            playerDirection = Direction.SOUTH
+            playerLocation = Pair(i, yMax)
+        } else if (line[i] == '#') {
+            blocks.add(Pair(i, yMax))
+        }
+    }
+    xMax = xMax.coerceAtLeast(line.lastIndex)
+    yMax++
+}
+val initialPosition = playerLocation.copy()
+while (isPositionInTheRoom(playerLocation, xMax, yMax)) {
+    visited.add(playerLocation)
+    if (checkForLoopIfObstacleInFront(playerLocation, playerDirection, history)) {
+        potentialBlocks.add(playerDirection.move(playerLocation))
+    }
+    history.add(MoveHistory(playerLocation, playerDirection))
+    val (newLocation, newDirection) = playerDirection.moveByPartOneRules(playerLocation, blocks)
+    playerLocation = newLocation
+    playerDirection = newDirection
+}
+
+println("Player location: ${visited.size}")
+println("Potential blocks: ${potentialBlocks.size}")
+
+fun checkForLoopIfObstacleInFront(
+    playerLocation: Pair<Int, Int>,
+    playerDirection: Direction,
+    history: MutableList<MoveHistory>
+): Boolean {
+    val potentialLocation = playerDirection.move(playerLocation)
+    val nextMove = playerDirection.moveByPartOneRules(playerLocation, blocks)
+    if (potentialLocation in visited || potentialLocation != nextMove.newLocation || !isPositionInTheRoom(potentialLocation, xMax, yMax)) {
+        return false
+    }
+    var localLocation = playerLocation
+    var localDirection = playerDirection
+    val localHistory = history.toMutableList()
+    val localBlocks = blocks.toMutableSet()
+    localBlocks.add(potentialLocation)
+    while (MoveHistory(localLocation, localDirection) !in localHistory) {
+        localHistory.add(MoveHistory(localLocation, localDirection))
+        val (newLocation, newDirection) = localDirection.moveByPartOneRules(localLocation, localBlocks)
+        localLocation = newLocation
+        localDirection = newDirection
+        if (!isPositionInTheRoom(localLocation, xMax, yMax)) {
+            return false
+        }
+    }
+    return true;
+}