Merge branch 'main' into day-18

Co-authored-by: Smaug123 <patrick+github@patrickstevens.co.uk>
Reviewed-on: #20

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>net8.0</TargetFramework>
@@ -13,6 +13,8 @@
     <Compile Include="Arithmetic.fs"/>
     <Compile Include="Rational.fs"/>
     <Compile Include="IntervalSet.fs" />
+    <Compile Include="Direction.fs" />
+    <Compile Include="List.fs" />
     <Compile Include="Day1.fs"/>
     <Compile Include="Day2.fs"/>
     <Compile Include="Day3.fs"/>
@@ -29,6 +31,7 @@
     <Compile Include="Day14.fs" />
     <Compile Include="Day15.fs" />
     <Compile Include="Day16.fs" />
+    <Compile Include="Day18.fs" />
     <Compile Include="Day19.fs" />
   </ItemGroup>
 

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Arr2D.fs

@@ -5,6 +5,7 @@
 #nowarn "9"
 #endif
 
+open System
 open Microsoft.FSharp.NativeInterop
 
 [<Struct>]
@@ -100,3 +101,76 @@ module Arr2D =
 #else
         NativePtr.initBlock a.Elements 0uy (uint32 sizeof<'a> * uint32 a.Length)
 #endif
+
+    /// Pass in a buffer of memory which we will use entirely for our own purposes (and may resize)
+    /// to maintain state.
+    /// `empty` is the value in empty cells; we will fill them with `fillWith`.
+    let floodFill
+        (stackBuf : ResizeArray<int>)
+        (s : Arr2D<'a>)
+        (empty : 'a)
+        (fillWith : 'a)
+        (currX : int)
+        (currY : int)
+        : unit
+        =
+        stackBuf.Clear ()
+        stackBuf.Add currX
+        stackBuf.Add currY
+
+        while stackBuf.Count > 0 do
+            let currY = stackBuf.[stackBuf.Count - 1]
+            stackBuf.RemoveAt (stackBuf.Count - 1)
+            let currX = stackBuf.[stackBuf.Count - 1]
+            stackBuf.RemoveAt (stackBuf.Count - 1)
+
+            if currX > 0 then
+                if get s (currX - 1) currY = empty then
+                    set s (currX - 1) currY fillWith
+                    stackBuf.Add (currX - 1)
+                    stackBuf.Add currY
+
+            if currX < s.Width - 1 then
+                if get s (currX + 1) currY = empty then
+                    set s (currX + 1) currY fillWith
+                    stackBuf.Add (currX + 1)
+                    stackBuf.Add currY
+
+            if currY > 0 then
+                if get s currX (currY - 1) = empty then
+                    set s currX (currY - 1) fillWith
+                    stackBuf.Add currX
+                    stackBuf.Add (currY - 1)
+
+            if currY < s.Height - 1 then
+                if get s currX (currY + 1) = empty then
+                    set s currX (currY + 1) fillWith
+                    stackBuf.Add currX
+                    stackBuf.Add (currY + 1)
+
+    /// SIMD go brr
+    let inline count< ^a when 'a : equality and 'a : unmanaged and 'a :> IEquatable<'a>>
+        (arr : Arr2D<'a>)
+        (x : 'a)
+        : int
+        =
+        let span =
+#if DEBUG
+            arr.Elements.AsSpan ()
+#else
+            ReadOnlySpan<'a> (NativePtr.toVoidPtr arr.Elements, arr.Length)
+#endif
+        MemoryExtensions.Count (span, x)
+
+    let print (arr : Arr2D<byte>) =
+        for row = 0 to arr.Height - 1 do
+            for col = 0 to arr.Width - 1 do
+                match get arr col row with
+                | 1uy -> printf "#"
+                | 0uy -> printf "."
+                | 2uy -> printf "O"
+                | _ -> failwith "bad"
+
+            printfn ""
+
+        printfn ""

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day10.fs

@@ -123,41 +123,6 @@ module Day10 =
 
         distance
 
-    let floodFill (stackBuf : ResizeArray<_>) (s : Arr2D<byte>) (currX : int) (currY : int) =
-        stackBuf.Clear ()
-        stackBuf.Add currX
-        stackBuf.Add currY
-
-        while stackBuf.Count > 0 do
-            let currY = stackBuf.[stackBuf.Count - 1]
-            stackBuf.RemoveAt (stackBuf.Count - 1)
-            let currX = stackBuf.[stackBuf.Count - 1]
-            stackBuf.RemoveAt (stackBuf.Count - 1)
-
-            if currX > 0 then
-                if Arr2D.get s (currX - 1) currY = 0uy then
-                    Arr2D.set s (currX - 1) currY 2uy
-                    stackBuf.Add (currX - 1)
-                    stackBuf.Add currY
-
-            if currX < s.Width - 1 then
-                if Arr2D.get s (currX + 1) currY = 0uy then
-                    Arr2D.set s (currX + 1) currY 2uy
-                    stackBuf.Add (currX + 1)
-                    stackBuf.Add currY
-
-            if currY > 0 then
-                if Arr2D.get s currX (currY - 1) = 0uy then
-                    Arr2D.set s currX (currY - 1) 2uy
-                    stackBuf.Add currX
-                    stackBuf.Add (currY - 1)
-
-            if currY < s.Height - 1 then
-                if Arr2D.get s currX (currY + 1) = 0uy then
-                    Arr2D.set s currX (currY + 1) 2uy
-                    stackBuf.Add currX
-                    stackBuf.Add (currY + 1)
-
     let print (s : Arr2D<byte>) =
         for y = 0 to s.Height - 1 do
             for x = 0 to s.Width - 1 do
@@ -310,12 +275,12 @@ module Day10 =
         let stackBuf = ResizeArray ()
 
         for line = 0 to system.Height - 1 do
-            floodFill stackBuf system 0 line
-            floodFill stackBuf system (system.Width - 1) line
+            Arr2D.floodFill stackBuf system 0uy 2uy 0 line
+            Arr2D.floodFill stackBuf system 0uy 2uy (system.Width - 1) line
 
         for col = 0 to system.Width - 1 do
-            floodFill stackBuf system col 0
-            floodFill stackBuf system col (system.Height - 1)
+            Arr2D.floodFill stackBuf system 0uy 2uy col 0
+            Arr2D.floodFill stackBuf system 0uy 2uy col (system.Height - 1)
 
         let mutable answer = 0
 

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day14.fs

@@ -137,19 +137,6 @@ module Day14 =
                 else // current = 0uy
                     pos <- pos + 1
 
-    let print (board : Arr2D<byte>) =
-        for row = 0 to board.Height - 1 do
-            for col = 0 to board.Width - 1 do
-                match Arr2D.get board col row with
-                | 0uy -> printf "."
-                | 1uy -> printf "O"
-                | 2uy -> printf "#"
-                | _ -> failwith "bad value"
-
-            printfn ""
-
-        printfn ""
-
     let score (board : Arr2D<byte>) =
         let mutable answer = 0ul
 

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

@@ -10,22 +10,8 @@ open System
 [<RequireQualifiedAccess>]
 module Day16 =
 
-    type Direction =
-        | Left = 0
-        | Right = 1
-        | Up = 2
-        | Down = 3
-
-    let inline dirToInt (d : Direction) =
-        match d with
-        | Direction.Left -> 0us
-        | Direction.Right -> 1us
-        | Direction.Up -> 2us
-        | Direction.Down -> 3us
-        | _ -> failwith "Bad"
-
     let inline storeDirectionAndPos (numCols : int) (col : int) (row : int) (direction : Direction) : uint16 =
-        4us * uint16 (col + numCols * row) + dirToInt direction
+        4us * uint16 (col + numCols * row) + Direction.toUInt direction
 
     let inline getDirection (input : uint16) =
         match input % 4us with

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day18.fs

@@ -0,0 +1,103 @@
+namespace AdventOfCode2023
+
+#if DEBUG
+#else
+#nowarn "9"
+#endif
+
+open System
+open System.Collections.Generic
+open System.Globalization
+
+[<RequireQualifiedAccess>]
+module Day18 =
+
+    let part1 (s : string) =
+        // Interleaved row and col
+        let mutable weHave = ResizeArray<int> ()
+        weHave.Add 0
+        weHave.Add 0
+
+        let mutable minCol = 0
+        let mutable maxCol = 0
+        let mutable minRow = 0
+        let mutable maxRow = 0
+
+        let mutable col = 0
+        let mutable row = 0
+        let mutable edgeCount = 0
+        use rows = StringSplitEnumerator.make '\n' s
+
+        for currRow in rows do
+            use mutable entries = StringSplitEnumerator.make' ' ' currRow
+            entries.MoveNext () |> ignore
+            let dir = Direction.ofChar entries.Current.[0]
+            entries.MoveNext () |> ignore
+
+            let distance =
+                Int32.Parse (entries.Current, NumberStyles.None, CultureInfo.InvariantCulture)
+
+            edgeCount <- edgeCount + distance
+
+            match dir with
+            | Direction.Down ->
+                for _ = 1 to distance do
+                    row <- row + 1
+                    weHave.Add row
+                    weHave.Add col
+
+                maxRow <- max row maxRow
+            | Direction.Up ->
+                for _ = 1 to distance do
+                    row <- row - 1
+                    weHave.Add row
+                    weHave.Add col
+
+                minRow <- min row minRow
+            | Direction.Left ->
+                for _ = 1 to distance do
+                    col <- col - 1
+                    weHave.Add row
+                    weHave.Add col
+
+                minCol <- min col minCol
+            | Direction.Right ->
+                for _ = 1 to distance do
+                    col <- col + 1
+                    weHave.Add row
+                    weHave.Add col
+
+                maxCol <- max col maxCol
+            | _ -> failwith "bad dir"
+
+        let buffer = Array.zeroCreate ((maxRow - minRow + 3) * (maxCol - minCol + 3))
+#if DEBUG
+        let system : Arr2D<byte> =
+            {
+                Elements = buffer
+                Width = maxCol - minCol + 3
+            }
+#else
+        use ptr = fixed buffer
+
+        let system : Arr2D<byte> =
+            {
+                Elements = ptr
+                Length = buffer.Length
+                Width = maxCol - minCol + 3
+            }
+#endif
+
+        let mutable pointIndex = 0
+
+        while pointIndex < weHave.Count do
+            let row = weHave.[pointIndex]
+            let col = weHave.[pointIndex + 1]
+            Arr2D.set system (col - minCol + 1) (row - minRow + 1) 1uy
+            pointIndex <- pointIndex + 2
+
+        Arr2D.floodFill (ResizeArray ()) system 0uy 2uy 0 0
+
+        Arr2D.count system 0uy + edgeCount
+
+    let part2 (s : string) = -1

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day19.fs

@@ -55,7 +55,8 @@ module Day19 =
                 | '<' -> true
                 | c -> failwith $"Bad comparison: %c{c}"
 
-            let operand = Int32.Parse (s.Slice (2, colon - 2), NumberStyles.None)
+            let operand =
+                Int32.Parse (s.Slice (2, colon - 2), NumberStyles.None, NumberFormatInfo.InvariantInfo)
 
             {
                 Component = comp
@@ -89,7 +90,7 @@ module Day19 =
                 None
         | _ -> failwith "bad component"
 
-    let rec compute (components : Dictionary<string, Rule ResizeArray * Dest>) x m a s (reg : string) =
+    let rec computePart1 (components : Dictionary<string, Rule ResizeArray * Dest>) x m a s (reg : string) =
         match components.TryGetValue reg with
         | false, _ -> failwith $"no rule matched: %s{reg}"
         | true, (rules, dest) ->
@@ -106,7 +107,7 @@ module Day19 =
                 | None -> i <- i + 1
 
             match result.Value with
-            | Register reg -> compute components x m a s reg
+            | Register reg -> computePart1 components x m a s reg
             | Accept -> true
             | Reject -> false
 
@@ -125,10 +126,7 @@ module Day19 =
 
         workflows
 
-    let part1 (s : string) =
-        use mutable rows = StringSplitEnumerator.make '\n' s
-        let workflows = readWorkflows &rows
-
+    let part1 (workflows : _) (rows : byref<StringSplitEnumerator>) =
         let mutable answer = 0
 
         for row in rows do
@@ -139,7 +137,8 @@ module Day19 =
                 let mutable s = 0
 
                 for comp in StringSplitEnumerator.make' ',' (row.Slice (1, row.Length - 2)) do
-                    let number = Int32.Parse (comp.Slice 2, NumberStyles.None)
+                    let number =
+                        Int32.Parse (comp.Slice 2, NumberStyles.None, NumberFormatInfo.InvariantInfo)
 
                     match comp.[0] with
                     | 'x' -> x <- number
@@ -148,7 +147,7 @@ module Day19 =
                     | 's' -> s <- number
                     | c -> failwith $"Bad char: %c{c}"
 
-                if compute workflows x m a s "in" then
+                if computePart1 workflows x m a s "in" then
                     answer <- answer + x + m + a + s
 
         answer
@@ -178,34 +177,134 @@ module Day19 =
         | _, AcceptanceCriterion.True -> AcceptanceCriterion.True
         | _, _ -> AcceptanceCriterion.Or (a, b)
 
-    let rec cata<'ret>
-        (atOr : 'ret -> 'ret -> 'ret)
-        (atAnd : 'ret -> 'ret -> 'ret)
-        (atFalse : unit -> 'ret)
-        (atTrue : unit -> 'ret)
-        (atBase : Component -> int -> int -> 'ret)
-        (ac : AcceptanceCriterion)
-        : 'ret
-        =
+    /// "low > high" means "empty interval"
+    [<Struct>]
+    type Interval =
+        {
+            Low : int
+            High : int
+        }
+
+        static member Empty =
+            {
+                Low = 1
+                High = 0
+            }
+
+    [<RequireQualifiedAccess>]
+    module Interval =
+        let size (i : Interval) =
+            if i.Low > i.High then 0 else i.High - i.Low + 1
+
+        let intersect (i1 : Interval) (i2 : Interval) =
+            if i1.Low > i1.High || i2.Low > i2.High then
+                i1
+            else if i1.High < i2.Low then
+                Interval.Empty
+            elif i2.High < i1.Low then
+                Interval.Empty
+            else
+                {
+                    Low = max i1.Low i2.Low
+                    High = min i1.High i2.High
+                }
+
+    type Conjunction =
+        {
+            X : Interval
+            M : Interval
+            A : Interval
+            S : Interval
+        }
+
+        static member All =
+            {
+                X =
+                    {
+                        Low = 1
+                        High = 4000
+                    }
+                M =
+                    {
+                        Low = 1
+                        High = 4000
+                    }
+                A =
+                    {
+                        Low = 1
+                        High = 4000
+                    }
+                S =
+                    {
+                        Low = 1
+                        High = 4000
+                    }
+            }
+
+    [<RequireQualifiedAccess>]
+    module Conjunction =
+        let conjAnd (c1 : Conjunction) (c2 : Conjunction) =
+            {
+                X = Interval.intersect c1.X c2.X
+                M = Interval.intersect c1.M c2.M
+                A = Interval.intersect c1.A c2.A
+                S = Interval.intersect c1.S c2.S
+            }
+
+        /// We rely on the intervals being disjoint by construction.
+        let size (x : Conjunction) : uint64 =
+            uint64 (Interval.size x.X)
+            * uint64 (Interval.size x.M)
+            * uint64 (Interval.size x.A)
+            * uint64 (Interval.size x.S)
+
+    type UnionOfConjunctions = Conjunction list
+
+    let rec toUnion (ac : AcceptanceCriterion) : UnionOfConjunctions =
         match ac with
-        | AcceptanceCriterion.False -> atFalse ()
-        | AcceptanceCriterion.True -> atTrue ()
-        | AcceptanceCriterion.Base (comp, low, high) -> atBase comp low high
-        | AcceptanceCriterion.And (a1, a2) ->
-            atAnd (cata atOr atAnd atFalse atTrue atBase a1) (cata atOr atAnd atFalse atTrue atBase a2)
-        | AcceptanceCriterion.Or (a1, a2) ->
-            atOr (cata atOr atAnd atFalse atTrue atBase a1) (cata atOr atAnd atFalse atTrue atBase a2)
-
-    type UnionOfConjunctions = (Component * int * int) list list
-
-    let toUnion (ac : AcceptanceCriterion) : UnionOfConjunctions =
-        cata
-            List.append
-            (fun l1 l2 -> [ List.concat (l1 @ l2) ])
-            (fun () -> failwith "no falses")
-            (fun () -> failwith "no trues")
-            (fun comp low high -> [ [ comp, low, high ] ])
-            ac
+        | Base (comp, low, high) ->
+            match comp with
+            | Component.A ->
+                { Conjunction.All with
+                    A =
+                        {
+                            Low = low
+                            High = high
+                        }
+                }
+            | Component.M ->
+                { Conjunction.All with
+                    M =
+                        {
+                            Low = low
+                            High = high
+                        }
+                }
+            | Component.S ->
+                { Conjunction.All with
+                    S =
+                        {
+                            Low = low
+                            High = high
+                        }
+                }
+            | Component.X ->
+                { Conjunction.All with
+                    X =
+                        {
+                            Low = low
+                            High = high
+                        }
+                }
+            | _ -> failwith "bad"
+            |> List.singleton
+        | And (a, b) ->
+            [
+                Conjunction.conjAnd (List.exactlyOne (toUnion a)) (List.exactlyOne (toUnion b))
+            ]
+        | Or (a, b) -> toUnion a @ toUnion b
+        | True -> failwith "already stripped out"
+        | False -> failwith "already stripped out"
 
     let rec acceptance
         (store : Dictionary<string, AcceptanceCriterion>)
@@ -219,56 +318,40 @@ module Day19 =
 
         let rules, final = workflows.[key]
 
-        let seed =
+        let mutable result =
             match final with
             | Register s -> acceptance store workflows s
             | Accept -> AcceptanceCriterion.True
             | Reject -> AcceptanceCriterion.False
 
-        let result =
-            (seed, Seq.rev rules)
-            ||> Seq.fold (fun crit rule ->
+        for i = rules.Count - 1 downto 0 do
+            let rule = rules.[i]
+
+            let cond =
+                if rule.IsLess then
+                    AcceptanceCriterion.Base (rule.Component, 1, rule.Operand - 1)
+                else
+                    AcceptanceCriterion.Base (rule.Component, rule.Operand + 1, 4000)
+
+            let negCond =
+                if rule.IsLess then
+                    AcceptanceCriterion.Base (rule.Component, rule.Operand, 4000)
+                else
+                    AcceptanceCriterion.Base (rule.Component, 1, rule.Operand)
+
+            result <-
                 match rule.Target with
-                | Register target ->
-                    let cond =
-                        if rule.IsLess then
-                            AcceptanceCriterion.Base (rule.Component, 1, rule.Operand - 1)
-                        else
-                            AcceptanceCriterion.Base (rule.Component, rule.Operand + 1, 4000)
-
-                    acOr (acAnd cond (acceptance store workflows target)) crit
-                | Accept ->
-                    let cond =
-                        if rule.IsLess then
-                            AcceptanceCriterion.Base (rule.Component, 1, rule.Operand - 1)
-                        else
-                            AcceptanceCriterion.Base (rule.Component, rule.Operand + 1, 4000)
-
-                    acOr cond crit
-                | Reject ->
-                    let negCond =
-                        if not rule.IsLess then
-                            AcceptanceCriterion.Base (rule.Component, 1, rule.Operand - 1)
-                        else
-                            AcceptanceCriterion.Base (rule.Component, rule.Operand + 1, 4000)
-
-                    acAnd negCond crit
-            )
+                | Register target -> acOr (acAnd cond (acceptance store workflows target)) (acAnd negCond result)
+                | Accept -> acOr cond (acAnd negCond result)
+                | Reject -> acAnd negCond result
 
         store.[key] <- result
         result
 
-    let part2 (s : string) =
-        use mutable rows = StringSplitEnumerator.make '\n' s
-        let workflows = readWorkflows &rows
-
+    let part2 (workflows : _) (rows : byref<StringSplitEnumerator>) : uint64 =
         let acceptanceRanges = Dictionary<string, AcceptanceCriterion> ()
 
         let a = acceptance acceptanceRanges workflows "in"
         let union = toUnion a
 
-        printfn "%+A" a
-        printfn "%+A" union
-
-        //uint64 (IntervalSet.count resolved.X) * uint64 (IntervalSet.count resolved.M) * uint64 (IntervalSet.count resolved.A) * uint64 (IntervalSet.count resolved.S)
-        0uL
+        union |> List.sumBy Conjunction.size

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Direction.fs

@@ -0,0 +1,24 @@
+namespace AdventOfCode2023
+
+type Direction =
+    | Left = 0
+    | Right = 1
+    | Up = 2
+    | Down = 3
+
+module Direction =
+    let inline toUInt (d : Direction) =
+        match d with
+        | Direction.Left -> 0us
+        | Direction.Right -> 1us
+        | Direction.Up -> 2us
+        | Direction.Down -> 3us
+        | _ -> failwith "Bad"
+
+    let inline ofChar (c : char) : Direction =
+        match c with
+        | 'L' -> Direction.Left
+        | 'R' -> Direction.Right
+        | 'U' -> Direction.Up
+        | 'D' -> Direction.Down
+        | c -> failwith $"Bad: %c{c}"

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/List.fs

@@ -0,0 +1,38 @@
+namespace AdventOfCode2023
+
+open System
+
+[<RequireQualifiedAccess>]
+module List =
+    let rec nTuples (n : int) (xs : 'a list) : 'a list list =
+#if DEBUG
+        if n < 0 then
+            raise (ArgumentException "n cannot be negative")
+#endif
+        match n, xs with
+        | 0, _ -> [ [] ]
+        | _, [] -> []
+        | _, x :: xs ->
+            let withX = nTuples (n - 1) xs |> List.map (fun xs -> x :: xs)
+            let withoutX = nTuples n xs
+            withX @ withoutX
+
+    let inline inclusionExclusion (sizeOf : 'a -> 'ret) (sizeOfTuple : 'a list -> 'ret) (xs : 'a list) : 'ret =
+        let mutable result = List.sumBy sizeOf xs
+        let mutable i = 2
+
+        while i <= xs.Length do
+            let nTuples = nTuples i xs
+            let sum = List.sumBy sizeOfTuple nTuples
+
+            if sum = LanguagePrimitives.GenericZero then
+                i <- Int32.MaxValue
+            else
+                if i % 2 = 0 then
+                    result <- result - sum
+                else
+                    result <- result + sum
+
+                i <- i + 1
+
+        result

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs

@@ -316,18 +316,46 @@ module Program =
             Console.WriteLine (part2.ToString ())
             Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
 
+        Console.WriteLine "=====Day 18====="
+
+        do
+            let input = Path.Combine (dir.FullName, "day18.txt") |> File.ReadAllText
+
+            sw.Restart ()
+            let part1 = Day18.part1 input
+            sw.Stop ()
+            Console.WriteLine (part1.ToString ())
+            Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
+            sw.Restart ()
+            let part2 = Day18.part2 input
+            sw.Stop ()
+            Console.WriteLine (part2.ToString ())
+            Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
+
         Console.WriteLine "=====Day 19====="
 
         do
             let input = Path.Combine (dir.FullName, "day19.txt") |> File.ReadAllText
 
             sw.Restart ()
-            let part1 = Day19.part1 input
+            use mutable s = StringSplitEnumerator.make '\n' input
+            let data = Day19.readWorkflows &s
+            sw.Stop ()
+
+            Console.Error.WriteLine (
+                (1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString ()
+                + "ms parse"
+            )
+
+            let mutable sCopy = s
+
+            sw.Restart ()
+            let part1 = Day19.part1 data &s
             sw.Stop ()
             Console.WriteLine (part1.ToString ())
             Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
             sw.Restart ()
-            let part2 = Day19.part2 input
+            let part2 = Day19.part2 data &sCopy
             sw.Stop ()
             Console.WriteLine (part2.ToString ())
             Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")

AdventOfCode2023.FSharp/Test/Test.fsproj

@@ -13,6 +13,7 @@
   <ItemGroup>
     <Compile Include="Util.fs"/>
     <Compile Include="TestIntervalSet.fs" />
+    <Compile Include="TestList.fs" />
     <Compile Include="TestDay1.fs"/>
     <Compile Include="TestDay2.fs"/>
     <Compile Include="TestDay3.fs"/>
@@ -29,6 +30,7 @@
     <Compile Include="TestDay14.fs" />
     <Compile Include="TestDay15.fs" />
     <Compile Include="TestDay16.fs" />
+    <Compile Include="TestDay18.fs" />
     <Compile Include="TestDay19.fs" />
     <EmbeddedResource Include="samples\day1.txt"/>
     <EmbeddedResource Include="samples\day1part1.txt"/>
@@ -49,6 +51,7 @@
     <EmbeddedResource Include="samples\day14.txt" />
     <EmbeddedResource Include="samples\day15.txt" />
     <EmbeddedResource Include="samples\day16.txt" />
+    <EmbeddedResource Include="samples\day18.txt" />
     <EmbeddedResource Include="samples\day19.txt" />
   </ItemGroup>
 

AdventOfCode2023.FSharp/Test/TestDay18.fs

@@ -0,0 +1,44 @@
+namespace AdventOfCode2023.Test
+
+open AdventOfCode2023
+open NUnit.Framework
+open FsUnitTyped
+open System.IO
+
+[<TestFixture>]
+module TestDay18 =
+
+    [<Test>]
+    let sample = Assembly.getEmbeddedResource typeof<Dummy>.Assembly "day18.txt"
+
+    [<Test>]
+    let part1Sample () = sample |> Day18.part1 |> shouldEqual 62
+
+    [<Test>]
+    let part2Sample () = sample |> Day18.part2 |> shouldEqual 0
+
+    [<Test>]
+    let part1Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day18.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day18.part1 s |> shouldEqual 106459
+
+    [<Test>]
+    let part2Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day18.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day18.part2 s |> shouldEqual 0

AdventOfCode2023.FSharp/Test/TestDay19.fs

@@ -7,17 +7,20 @@ open System.IO
 
 [<TestFixture>]
 module TestDay19 =
-
     [<Test>]
     let sample = Assembly.getEmbeddedResource typeof<Dummy>.Assembly "day19.txt"
 
     [<Test>]
     let part1Sample () =
-        sample |> Day19.part1 |> shouldEqual 19114
+        use mutable s = StringSplitEnumerator.make '\n' sample
+        let workflows = Day19.readWorkflows &s
+        Day19.part1 workflows &s |> shouldEqual 19114
 
     [<Test>]
     let part2Sample () =
-        sample |> Day19.part2 |> shouldEqual 167409079868000uL
+        use mutable s = StringSplitEnumerator.make '\n' sample
+        let workflows = Day19.readWorkflows &s
+        Day19.part2 workflows &s |> shouldEqual 167409079868000uL
 
     [<Test>]
     let part1Actual () =
@@ -30,7 +33,10 @@ module TestDay19 =
                 Assert.Inconclusive ()
                 failwith "unreachable"
 
-        Day19.part1 s |> shouldEqual 368964
+        use mutable s = StringSplitEnumerator.make '\n' s
+        let workflows = Day19.readWorkflows &s
+
+        Day19.part1 workflows &s |> shouldEqual 368964
 
     [<Test>]
     let part2Actual () =
@@ -43,4 +49,7 @@ module TestDay19 =
                 Assert.Inconclusive ()
                 failwith "unreachable"
 
-        Day19.part2 s |> shouldEqual 8314uL
+        use mutable s = StringSplitEnumerator.make '\n' s
+        let workflows = Day19.readWorkflows &s
+
+        Day19.part2 workflows &s |> shouldEqual 127675188176682uL

AdventOfCode2023.FSharp/Test/TestList.fs

@@ -0,0 +1,20 @@
+namespace Test
+
+open NUnit.Framework
+open FsUnitTyped
+open FsCheck
+open AdventOfCode2023
+
+[<TestFixture>]
+module TestList =
+
+    [<Test>]
+    let ``n-tuples have the right length`` () =
+        let property (n : int) (xs : char list) =
+            let n = min (abs n) 6
+            let xs = xs |> List.take (min 10 xs.Length)
+            let tuples = List.nTuples n xs
+            tuples |> List.forall (fun i -> i.Length = n)
+
+        property 1 [ 'v' ] |> shouldEqual true
+        Check.QuickThrowOnFailure property

AdventOfCode2023.FSharp/Test/samples/day18.txt

@@ -0,0 +1,14 @@
+R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)