@@ -10,42 +10,36 @@ object Day17:
1010 Set (Point (0 , 0 ), Point (0 , 1 ), Point (0 , 2 ), Point (0 , 3 )),
1111 Set (Point (0 , 0 ), Point (1 , 0 ), Point (0 , 1 ), Point (1 , 1 )))
1212
13- case class Point (x : Int , y : Int ):
14- def + (other : Point ): Point = Point (x + other.x, y + other.y)
13+ extension (shape : Set [Point ])
14+ def move (dx : Int , dy : Int ): Set [Point ] = shape.map(p => Point (p.x + dx, p.y + dy))
15+ def canMove (grid : Set [Point ]): Boolean = shape.forall(p => p.x > 0 && p.x < 8 && ! grid.contains(p))
1516
16- case class State (grid : Set [Point ], wind : String , shapeIndex : Int , windIndex : Int , height : Int )
17+ case class Point (x : Int , y : Int )
18+ case class State (grid : Set [Point ], shapeIndex : Int , jetIndex : Int , height : Int )
1719
1820 @ tailrec
19- def fall (grid : Set [Point ], shape : Set [Point ], wind : String , windIndex : Int ): (Int , Set [Point ]) =
20- var next = shape
21+ def fall (grid : Set [Point ], shape : Set [Point ], jets : String , jetIndex : Int ): (Set [Point ], Int ) =
22+ val jet = jets(jetIndex % jets.length)
23+ val first = if jet == '>' then shape.move(1 , 0 ) else shape.move(- 1 , 0 )
24+ val second = if first.canMove(grid) then first else shape
25+ val third = second.move(0 , - 1 )
26+ if third.canMove(grid) then fall(grid, third, jets, jetIndex + 1 ) else (second, jetIndex + 1 )
2127
22- val gust = wind(windIndex % wind.size)
23- val shift = if gust == '>' then Point (1 , 0 ) else Point (- 1 , 0 )
24- var test = shape.map(_ + shift)
25- if test.forall(p => p.x > 0 && p.x < 8 && ! grid.contains(p)) then next = test
28+ def step (jets : String )(state : State ): State =
29+ val State (grid, shapeIndex, jetIndex, height) = state
30+ val initialShape = shapes(shapeIndex % shapes.size).move(3 , height + 4 )
31+ val (nextShape, nextJetIndex) = fall(grid, initialShape, jets, jetIndex)
32+ State (grid ++ nextShape, shapeIndex + 1 , nextJetIndex, height.max(nextShape.map(_.y).max))
2633
27- test = next.map(_ + Point ( 0 , - 1 ))
28- if test.exists(grid.contains) then (windIndex + 1 , next) else fall(grid, test, wind, windIndex + 1 )
29- end fall
34+ def simulate ( jets : String ) : Iterator [ Int ] =
35+ val initial = State ( Set .tabulate( 8 )( Point (_, 0 )), 0 , 0 , 0 )
36+ Iterator .iterate(initial)(step(jets)).map(_.height)
3037
31- def step (state : State ): State =
32- val State (grid, wind, shapeIndex, windIndex, height) = state
33- val initial = Point (3 , height + 4 )
34- val next = shapes(shapeIndex % shapes.size).map(_ + initial)
35- val (nextWindIndex, foo) = fall(grid, next, wind, windIndex)
36- 37- State (grid ++ foo, wind, shapeIndex + 1 , nextWindIndex, height.max(foo.map(_.y).max))
38- end step
39- 40- def simulate (input : String ): Iterator [State ] =
41- val initial = State (Set .tabulate(8 )(Point (_, 0 )), input, 0 , 0 , 0 )
42- Iterator .iterate(initial)(step)
43- 44- def part1 (input : String ): Int = simulate(input).drop(2022 ).next().height
38+ def part1 (input : String ): Int = simulate(input).drop(2022 ).next()
4539
4640 def part2 (input : String ): Long =
4741 val guess = 1000
48- val height = simulate(input).drop( 1 ).take( 10 * guess).map(_.height ).toSeq
42+ val height = simulate(input).slice( 1 , 10 * guess).toSeq
4943 val delta = height.sliding(2 ).map { case Seq (a, b) => b - a }.toSeq
5044 val index = delta.lastIndexOfSlice(delta.takeRight(guess), delta.size - guess - 1 )
5145 val cycleHeight = height(delta.size - guess) - height(index)
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