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Update 2023 day 17 to simplify State and use heatloss Map #514

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Dec 29, 2023
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Update 2023 day 17 to simplify State and use heatloss Map #514

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44 changes: 21 additions & 23 deletions 2023/src/day17.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -36,58 +36,56 @@ val xRange = grid.head.indices
val yRange = grid.indices

case class Point(x: Int, y: Int):
def inBounds = xRange.contains(x) && yRange.contains(y)

def move(dir: Dir) = dir match
case Dir.N => copy(y = y - 1)
case Dir.S => copy(y = y + 1)
case Dir.E => copy(x = x + 1)
case Dir.W => copy(x = x - 1)

def inBounds(p: Point) =
xRange.contains(p.x) && yRange.contains(p.y)

def heatLoss(p: Point) =
if p.inBounds then grid(p.y)(p.x) else 0
if inBounds(p) then grid(p.y)(p.x) else 0

case class State(pos: Point, dir: Dir, streak: Int, totalHeatLoss: Int):
case class State(pos: Point, dir: Dir, streak: Int):
def straight: State =
val newPos = pos.move(dir)
State(pos.move(dir), dir, streak + 1, totalHeatLoss + heatLoss(newPos))
State(pos.move(dir), dir, streak + 1)

def turnLeft: State =
val newDir = dir.turnLeft
val newPos = pos.move(newDir)
State(newPos, newDir, 1, totalHeatLoss + heatLoss(newPos))
State(pos.move(newDir), newDir, 1)

def turnRight: State =
val newDir = dir.turnRight
val newPos = pos.move(newDir)
State(pos.move(newDir), newDir, 1, totalHeatLoss + heatLoss(newPos))
State(pos.move(newDir), newDir, 1)

def nextStates: List[State] =
List(straight, turnLeft, turnRight).filter: s =>
s.pos.inBounds && s.streak <= 3
inBounds(s.pos) && s.streak <= 3

def nextStates2: List[State] =
if streak < 4 then List(straight)
else List(straight, turnLeft, turnRight).filter: s =>
s.pos.inBounds && s.streak <= 10

def motion = (pos, dir, streak)
inBounds(s.pos) && s.streak <= 10

def search(next: State => List[State]): Int =
import collection.mutable.{PriorityQueue, Set}
import collection.mutable.{PriorityQueue, Map}

val minHeatLoss = Map.empty[State, Int]

given Ordering[State] = Ordering.by(_.totalHeatLoss)
given Ordering[State] = Ordering.by(minHeatLoss)
val pq = PriorityQueue.empty[State].reverse

var visiting = State(Point(0, 0), Dir.E, 0, 0)
val visited = Set(visiting.motion)
var visiting = State(Point(0, 0), Dir.E, 0)
minHeatLoss(visiting) = 0

val end = Point(xRange.max, yRange.max)
while visiting.pos != end do
val states = next(visiting).filterNot(s => visited(s.motion))
states.foreach(s => s"enqueuing: $s")
pq.enqueue(states*)
visited ++= states.map(_.motion)
val states = next(visiting).filterNot(minHeatLoss.contains)
states.foreach: s =>
minHeatLoss(s) = minHeatLoss(visiting) + heatLoss(s.pos)
pq.enqueue(s)
visiting = pq.dequeue()

visiting.totalHeatLoss
minHeatLoss(visiting)