Part 1

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day16.fs

@@ -1,15 +1,205 @@
 namespace AdventOfCode2023
 
+#if DEBUG
+#else
+#nowarn "9"
+#endif
+
 open System
+open System.Collections.Generic
 open System.Globalization
 
 [<RequireQualifiedAccess>]
 module Day16 =
 
+    [<Struct>]
+    type Direction =
+        | Left
+        | Right
+        | Up
+        | Down
+
+    let inline dirToInt (d : Direction) =
+        match d with
+        | Left -> 0us
+        | Right -> 1us
+        | Up -> 2us
+        | Down -> 3us
+
+    let inline storeDirectionAndPos (numCols : int) (col : int) (row : int) (direction : Direction) : uint16 =
+        4us * uint16 (col + numCols * row) + dirToInt direction
+
+    let inline getDirection (input : uint16) =
+        match input % 4us with
+        | 0us -> Direction.Left
+        | 1us -> Direction.Right
+        | 2us -> Direction.Up
+        | 3us -> Direction.Down
+        | _ -> failwith "bad"
+
+    let inline getCol (numCols : int) (input : uint16) =
+        (input / 4us) % uint16 numCols
+        |> int
+
+    let inline getRow (numCols : int) (input : uint16) =
+        (input / 4us) / uint16 numCols
+        |> int
+
+    let maxEncoded (numCols : int) (numRows : int) : uint16 =
+        4us * uint16 ((numCols - 1) + numCols * (numRows - 1)) + 3us
+
+    let inline getAt (numCols : int) (s : string) (row : int) (col : int) =
+        s.[row * (numCols + 1) + col]
+
+    let printArr (arr : Arr2D<bool>) =
+        for row = 0 to arr.Height - 1 do
+            for col = 0 to arr.Width - 1 do
+                if Arr2D.get arr col row then printf "#" else printf "."
+            printfn ""
+        printfn ""
+
     let part1 (s : string) =
-        use lines = StringSplitEnumerator.make '\n' s
-        answer
+        let numLines = s.AsSpan().Count '\n'
+        let numCols = s.IndexOf '\n'
+        let arr = Array.zeroCreate (numLines * numCols)
+#if DEBUG
+        let arr : Arr2D<bool> =
+            {
+                Elements = arr
+                Width = numCols
+            }
+#else
+        use ptr = fixed arr
+        let arr : Arr2D<bool> =
+            {
+                Elements = arr
+                Width = numCols
+                Length = arr.Count
+            }
+#endif
+        let going = ResizeArray ()
+        going.Add (storeDirectionAndPos numCols LanguagePrimitives.GenericZero LanguagePrimitives.GenericZero Direction.Right)
+        let seen = Array.zeroCreate (int (maxEncoded numCols numLines))
+
+        while going.Count > 0 do
+            let nextUp = going.[going.Count - 1]
+            match seen.[int nextUp] with
+            | true ->
+                going.RemoveAt (going.Count - 1)
+            | false ->
+            seen.[int nextUp] <- true
+            let col = getCol numCols nextUp
+            let row = getRow numCols nextUp
+            let dir = getDirection nextUp
+            Arr2D.set arr col row true
+            match dir with
+            | Direction.Right ->
+                match getAt numCols s row col with
+                | '-'
+                | '.' ->
+                    if col < arr.Width - 1 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols (col + 1) row dir
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '/' ->
+                    if row > 0 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols col (row - 1) Direction.Up
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '\\' ->
+                    if row < numLines - 1 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols col (row + 1) Direction.Down
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '|' ->
+                    going.RemoveAt (going.Count - 1)
+                    if row < numLines - 1 then
+                        going.Add (storeDirectionAndPos numCols col (row + 1) Direction.Down)
+                    if row > 0 then
+                        going.Add (storeDirectionAndPos numCols col (row - 1) Direction.Up)
+                | c ->
+                    failwith $"Unrecognised char: %c{c}"
+            | Direction.Left ->
+                match getAt numCols s row col with
+                | '-'
+                | '.' ->
+                    if col > 0 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols (col - 1) row dir
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '\\' ->
+                    if row > 0 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols col (row - 1) Direction.Up
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '/' ->
+                    if row < numLines - 1 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols col (row + 1) Direction.Down
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '|' ->
+                    going.RemoveAt (going.Count - 1)
+                    if row < numLines - 1 then
+                        going.Add (storeDirectionAndPos numCols col (row + 1) Direction.Down)
+                    if row > 0 then
+                        going.Add (storeDirectionAndPos numCols col (row - 1) Direction.Up)
+                | c ->
+                    failwith $"Unrecognised char: %c{c}"
+            | Direction.Up ->
+                match getAt numCols s row col with
+                | '|'
+                | '.' ->
+                    if row > 0 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols col (row - 1) dir
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '/' ->
+                    if col < numCols - 1 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols (col + 1) row Direction.Right
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '\\' ->
+                    if col > 0 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols (col - 1) row Direction.Left
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '-' ->
+                    going.RemoveAt (going.Count - 1)
+                    if col < numCols - 1 then
+                        going.Add (storeDirectionAndPos numCols (col + 1) row Direction.Right)
+                    if col > 0 then
+                        going.Add (storeDirectionAndPos numCols (col - 1) row Direction.Left)
+                | c ->
+                    failwith $"Unrecognised char: %c{c}"
+            | Direction.Down ->
+                match getAt numCols s row col with
+                | '|'
+                | '.' ->
+                    if row < arr.Height - 1 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols col (row + 1) dir
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '\\' ->
+                    if col < numCols - 1 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols (col + 1) row Direction.Right
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '/' ->
+                    if col > 0 then
+                        going.[going.Count - 1] <- storeDirectionAndPos numCols (col - 1) row Direction.Left
+                    else
+                        going.RemoveAt (going.Count - 1)
+                | '-' ->
+                    going.RemoveAt (going.Count - 1)
+                    if col < numCols - 1 then
+                        going.Add (storeDirectionAndPos numCols (col + 1) row Direction.Right)
+                    if col > 0 then
+                        going.Add (storeDirectionAndPos numCols (col - 1) row Direction.Left)
+                | c ->
+                    failwith $"Unrecognised char: %c{c}"
+
+        arr.Elements.AsSpan().Count true
 
     let part2 (s : string) =
         use lines = StringSplitEnumerator.make '\n' s
-        answer
+        0

AdventOfCode2023.FSharp/Test/TestDay16.fs

@@ -13,11 +13,11 @@ module TestDay16 =
 
     [<Test>]
     let part1Sample () =
-        sample |> Day16.part1 |> shouldEqual 1320
+        sample |> Day16.part1 |> shouldEqual 46
 
     [<Test>]
     let part2Sample () =
-        sample |> Day16.part2 |> shouldEqual 145ul
+        sample |> Day16.part2 |> shouldEqual 51
 
     [<Test>]
     let part1Actual () =
@@ -30,7 +30,7 @@ module TestDay16 =
                 Assert.Inconclusive ()
                 failwith "unreachable"
 
-        Day16.part1 s |> shouldEqual 521434
+        Day16.part1 s |> shouldEqual 8112
 
     [<Test>]
     let part2Actual () =
@@ -43,4 +43,4 @@ module TestDay16 =
                 Assert.Inconclusive ()
                 failwith "unreachable"
 
-        Day16.part2 s |> shouldEqual 248279ul
+        Day16.part2 s |> shouldEqual 0

AdventOfCode2023.FSharp/Test/samples/day16.txt

@@ -0,0 +1,10 @@
+.|...\....
+|.-.\.....
+.....|-...
+........|.
+..........
+.........\
+..../.\\..
+.-.-/..|..
+.|....-|.\
+..//.|....