Day 14: Parabolic Reflector Dish

Megathread guidelines

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  • cvttsd2si
    5·
    1 year ago

    Scala3

    type Grid = List[List[Char]]

def tiltUp(a: Grid): Grid = 
    @tailrec def go(c: List[Char], acc: List[Char]): List[Char] =
        def shifted(c: List[Char]) = 
            val (h, t) = c.splitAt(c.count(_ == 'O'))
            h.map(_ => 'O') ++ t.map(_ => '.') ++ acc
        val d = c.indexOf('#')
        if d == -1 then shifted(c) else go(c.slice(d + 1, c.size), '#'::shifted(c.slice(0, d)))
        
    a.map(go(_, List()).reverse)

def weight(a: Grid): Long = a.map(d => d.zipWithIndex.filter((c, _) => c == 'O').map(1 + _._2).sum).sum
def rotateNeg90(a: Grid): Grid = a.reverse.transpose
def runCycle = Seq.fill(4)(tiltUp andThen rotateNeg90).reduceLeft(_ andThen _)

def stateAt(target: Long, a: Grid): Grid =
    @tailrec def go(cycle: Int, state: Grid, seen: Map[Grid, Int]): Grid =
        seen.get(state) match
            case Some(i) => if (target - cycle) % (cycle - i) == 0 then state else go(cycle + 1, runCycle(state), seen)
            case None => go(cycle + 1, runCycle(state), seen + (state -> cycle))
    
    go(0, a, Map())

def toColMajorGrid(a: List[String]): Grid = rotateNeg90(a.map(_.toList))

def task1(a: List[String]): Long = weight(tiltUp(toColMajorGrid(a)))
def task2(a: List[String]): Long = weight(stateAt(1_000_000_000, toColMajorGrid(a)))