Dead

.gitignore

@@ -10,3 +10,4 @@ result
 .profile*
 
 inputs/
+AdventOfCode2023.FSharp/Test/TestResults/

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

@@ -12,6 +12,8 @@
     <Compile Include="EfficientString.fs"/>
     <Compile Include="Arithmetic.fs"/>
     <Compile Include="Rational.fs"/>
+    <Compile Include="IntervalSet.fs" />
+    <Compile Include="List.fs" />
     <Compile Include="Day1.fs"/>
     <Compile Include="Day2.fs"/>
     <Compile Include="Day3.fs"/>
@@ -28,6 +30,7 @@
     <Compile Include="Day14.fs" />
     <Compile Include="Day15.fs" />
     <Compile Include="Day16.fs" />
+    <Compile Include="Day19.fs" />
   </ItemGroup>
 
 </Project>

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

@@ -0,0 +1,363 @@
+namespace AdventOfCode2023
+
+open System
+open System.Collections.Generic
+open System.Globalization
+
+[<RequireQualifiedAccess>]
+module Day19 =
+
+    type Component =
+        | X = 0
+        | M = 1
+        | A = 2
+        | S = 3
+
+    [<RequireQualifiedAccess>]
+    module Component =
+        let ofChar (c : char) : Component =
+            match c with
+            | 'x' -> Component.X
+            | 'm' -> Component.M
+            | 'a' -> Component.A
+            | 's' -> Component.S
+            | c -> failwith $"bad component: %c{c}"
+
+    type Dest =
+        | Register of string
+        | Accept
+        | Reject
+
+        static member OfString (s : EfficientString) : Dest =
+            if s.Length = 1 && s.[0] = 'A' then Dest.Accept
+            elif s.Length = 1 && s.[0] = 'R' then Dest.Reject
+            else Dest.Register (s.ToString ())
+
+    type Rule =
+        {
+            Component : Component
+            IsLess : bool
+            Operand : int
+            Target : Dest
+        }
+
+        static member OfString (s : EfficientString) : Choice<Rule, Dest> =
+            match s.IndexOf ':' with
+            | -1 -> Choice2Of2 (Dest.OfString (s.Slice (0, s.Length)))
+            | colon ->
+
+            let dest = Dest.OfString (s.Slice (colon + 1))
+            let comp = Component.ofChar s.[0]
+
+            let isLess =
+                match s.[1] with
+                | '>' -> false
+                | '<' -> true
+                | c -> failwith $"Bad comparison: %c{c}"
+
+            let operand =
+                Int32.Parse (s.Slice (2, colon - 2), NumberStyles.None, NumberFormatInfo.InvariantInfo)
+
+            {
+                Component = comp
+                IsLess = isLess
+                Target = dest
+                Operand = operand
+            }
+            |> Choice1Of2
+
+    let inline matches (rule : Rule) x m a s =
+        match rule.Component with
+        | Component.A ->
+            if (rule.IsLess && a < rule.Operand) || (not rule.IsLess && a > rule.Operand) then
+                Some rule.Target
+            else
+                None
+        | Component.X ->
+            if (rule.IsLess && x < rule.Operand) || (not rule.IsLess && x > rule.Operand) then
+                Some rule.Target
+            else
+                None
+        | Component.M ->
+            if (rule.IsLess && m < rule.Operand) || (not rule.IsLess && m > rule.Operand) then
+                Some rule.Target
+            else
+                None
+        | Component.S ->
+            if (rule.IsLess && s < rule.Operand) || (not rule.IsLess && s > rule.Operand) then
+                Some rule.Target
+            else
+                None
+        | _ -> failwith "bad component"
+
+    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) ->
+            let mutable result = ValueNone
+            let mutable i = 0
+
+            while result.IsNone do
+                if i = rules.Count then
+                    result <- ValueSome dest
+                else
+
+                match matches rules.[i] x m a s with
+                | Some dest -> result <- ValueSome dest
+                | None -> i <- i + 1
+
+            match result.Value with
+            | Register reg -> computePart1 components x m a s reg
+            | Accept -> true
+            | Reject -> false
+
+    let readWorkflows (rows : byref<StringSplitEnumerator>) =
+        let workflows = Dictionary<string, Rule ResizeArray * Dest> ()
+
+        while rows.MoveNext () && not rows.Current.IsEmpty do
+            let brace = rows.Current.IndexOf '{'
+            let name = rows.Current.Slice(0, brace).ToString ()
+            let rules = ResizeArray ()
+
+            for rule in StringSplitEnumerator.make' ',' (rows.Current.Slice(brace + 1).TrimEnd '}') do
+                match Rule.OfString rule with
+                | Choice1Of2 rule -> rules.Add rule
+                | Choice2Of2 dest -> workflows.[name] <- (rules, dest)
+
+        workflows
+
+    let part1 (s : string) =
+        use mutable rows = StringSplitEnumerator.make '\n' s
+        let workflows = readWorkflows &rows
+
+        let mutable answer = 0
+
+        for row in rows do
+            if not row.IsEmpty then
+                let mutable x = 0
+                let mutable m = 0
+                let mutable a = 0
+                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, NumberFormatInfo.InvariantInfo)
+
+                    match comp.[0] with
+                    | 'x' -> x <- number
+                    | 'm' -> m <- number
+                    | 'a' -> a <- number
+                    | 's' -> s <- number
+                    | c -> failwith $"Bad char: %c{c}"
+
+                if computePart1 workflows x m a s "in" then
+                    answer <- answer + x + m + a + s
+
+        answer
+
+    type AcceptanceCriterion =
+        | True
+        | False
+        | Base of Component * low : int * high : int
+        | And of AcceptanceCriterion * AcceptanceCriterion
+        | Or of AcceptanceCriterion * AcceptanceCriterion
+
+    let rec acAnd a b =
+        match a, b with
+        | AcceptanceCriterion.Or (a1, a2), _ -> AcceptanceCriterion.Or (acAnd a1 b, acAnd a2 b)
+        | AcceptanceCriterion.True, _ -> b
+        | AcceptanceCriterion.False, _ -> False
+        | _, AcceptanceCriterion.Or (b1, b2) -> AcceptanceCriterion.Or (acAnd a b1, acAnd a b2)
+        | _, AcceptanceCriterion.True -> a
+        | _, AcceptanceCriterion.False -> False
+        | _, _ -> AcceptanceCriterion.And (a, b)
+
+    let inline acOr a b =
+        match a, b with
+        | AcceptanceCriterion.False, _ -> b
+        | AcceptanceCriterion.True, _ -> AcceptanceCriterion.True
+        | _, AcceptanceCriterion.False -> a
+        | _, AcceptanceCriterion.True -> AcceptanceCriterion.True
+        | _, _ -> AcceptanceCriterion.Or (a, b)
+
+    /// "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
+        | 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>)
+        (workflows : Dictionary<string, ResizeArray<Rule> * Dest>)
+        (key : string)
+        : AcceptanceCriterion
+        =
+        match store.TryGetValue key with
+        | true, v -> v
+        | false, _ ->
+
+        let rules, final = workflows.[key]
+
+        let mutable result =
+            match final with
+            | Register s -> acceptance store workflows s
+            | Accept -> AcceptanceCriterion.True
+            | Reject -> AcceptanceCriterion.False
+
+        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 -> 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) : uint64 =
+        use mutable rows = StringSplitEnumerator.make '\n' s
+        let workflows = readWorkflows &rows
+
+        let acceptanceRanges = Dictionary<string, AcceptanceCriterion> ()
+
+        let a = acceptance acceptanceRanges workflows "in"
+        let union = toUnion a
+
+        union |> List.sumBy Conjunction.size

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/IntervalSet.fs

@@ -0,0 +1,70 @@
+namespace AdventOfCode2023
+
+type IntervalSet = private | IntervalSet of (int * int) list
+
+[<RequireQualifiedAccess>]
+module IntervalSet =
+    let empty = IntervalSet []
+
+    let private add' (low : int) (high : int) intervals : _ list =
+        let rec go (low : int) (high : int) (intervals : (int * int) list) =
+            match intervals with
+            | [] -> [ low, high ]
+            | (lowExisting, highExisting) :: intervals ->
+                if low > highExisting then
+                    (lowExisting, highExisting) :: go low high intervals
+                elif high < lowExisting then
+                    (low, high) :: (lowExisting, highExisting) :: intervals
+                elif high = lowExisting then
+                    (low, highExisting) :: intervals
+                elif high <= highExisting then
+                    (min low lowExisting, highExisting) :: intervals
+                else
+                    // low <= highExisting, highExisting < high
+                    (min low lowExisting, highExisting) :: go (highExisting + 1) high intervals
+
+        go low high intervals
+
+    let add (low : int) (high : int) (IntervalSet intervals) : IntervalSet = add' low high intervals |> IntervalSet
+
+    let contains (x : int) (IntervalSet intervals) : bool =
+        let rec go (intervals : (int * int) list) =
+            match intervals with
+            | [] -> false
+            | (low, high) :: intervals ->
+                if low > x then false
+                elif x <= high then true
+                else go intervals
+
+        go intervals
+
+    let private union' i1 i2 =
+        (i2, i1) ||> List.fold (fun i (low, high) -> add' low high i)
+
+    let union (IntervalSet i1) (IntervalSet i2) : IntervalSet = union' i1 i2 |> IntervalSet
+
+    let private intersectionHelper (low : int) (high : int) (ints : (int * int) list) =
+        let rec go (low : int) (high : int) (ints : (int * int) list) =
+            match ints with
+            | [] -> []
+            | (lowExisting, highExisting) :: ints ->
+                if low > highExisting then
+                    go low high ints
+                elif high < lowExisting then
+                    []
+                elif high <= highExisting then
+                    [ max low lowExisting, high ]
+                else
+                    (max low lowExisting, highExisting) :: go (highExisting + 1) high ints
+
+        go low high ints
+
+    let private intersection' i1 i2 =
+        // a int (b U c) = (a int b) U (a int c)
+        ([], i1)
+        ||> List.fold (fun soFar (low, high) -> union' soFar (intersectionHelper low high i2))
+
+    let intersection (IntervalSet i1) (IntervalSet i2) : IntervalSet = intersection' i1 i2 |> IntervalSet
+
+    let count (IntervalSet i) =
+        i |> List.sumBy (fun (low, high) -> high - low + 1)

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

@@ -316,6 +316,22 @@ module Program =
             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
+            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
+            sw.Stop ()
+            Console.WriteLine (part2.ToString ())
+            Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
+
         endToEnd.Stop ()
 
         Console.Error.WriteLine (

AdventOfCode2023.FSharp/Test/Test.fsproj

@@ -5,10 +5,15 @@
 
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
+
+    <EnableStaticNativeInstrumentation>False</EnableStaticNativeInstrumentation>
+    <EnableDynamicNativeInstrumentation>False</EnableDynamicNativeInstrumentation>
   </PropertyGroup>
 
   <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"/>
@@ -25,6 +30,7 @@
     <Compile Include="TestDay14.fs" />
     <Compile Include="TestDay15.fs" />
     <Compile Include="TestDay16.fs" />
+    <Compile Include="TestDay19.fs" />
     <EmbeddedResource Include="samples\day1.txt"/>
     <EmbeddedResource Include="samples\day1part1.txt"/>
     <EmbeddedResource Include="samples\day2.txt"/>
@@ -44,11 +50,14 @@
     <EmbeddedResource Include="samples\day14.txt" />
     <EmbeddedResource Include="samples\day15.txt" />
     <EmbeddedResource Include="samples\day16.txt" />
+    <EmbeddedResource Include="samples\day19.txt" />
   </ItemGroup>
 
   <ItemGroup>
+    <PackageReference Include="FsCheck" Version="2.16.6" />
     <PackageReference Include="FsUnit" Version="5.6.1"/>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.0"/>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0"/>
+    <PackageReference Include="Microsoft.CodeCoverage" Version="17.8.0"/>
     <PackageReference Include="NUnit3TestAdapter" Version="4.2.1"/>
     <PackageReference Include="NUnit.Analyzers" Version="3.6.1"/>
     <PackageReference Include="coverlet.collector" Version="6.0.0"/>

AdventOfCode2023.FSharp/Test/TestDay19.fs

@@ -0,0 +1,45 @@
+namespace AdventOfCode2023.Test
+
+open AdventOfCode2023
+open NUnit.Framework
+open FsUnitTyped
+open System.IO
+
+[<TestFixture>]
+module TestDay19 =
+    [<Test>]
+    let sample = Assembly.getEmbeddedResource typeof<Dummy>.Assembly "day19.txt"
+
+    [<Test>]
+    let part1Sample () =
+        sample |> Day19.part1 |> shouldEqual 19114
+
+    [<Test>]
+    let part2Sample () =
+        sample |> Day19.part2 |> shouldEqual 167409079868000uL
+
+    [<Test>]
+    let part1Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day19.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day19.part1 s |> shouldEqual 368964
+
+    [<Test>]
+    let part2Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day19.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day19.part2 s |> shouldEqual 127675188176682uL

AdventOfCode2023.FSharp/Test/TestIntervalSet.fs

@@ -0,0 +1,86 @@
+namespace AdventOfCode2023.Test
+
+open System.Threading
+open AdventOfCode2023
+open NUnit.Framework
+open FsUnitTyped
+open FsCheck
+
+[<TestFixture>]
+module TestIntervalSet =
+
+    /// Normalises e.g. (5, 3) to (3, 5) too.
+    let toIntervalSet (model : (int * int) list) =
+        (IntervalSet.empty, model)
+        ||> List.fold (fun intervals (x1, x2) -> IntervalSet.add (min x1 x2) (max x1 x2) intervals)
+
+    let modelContains (x : int) (model : (int * int) list) =
+        model
+        |> List.exists (fun (x1, x2) ->
+            let x1, x2 = min x1 x2, max x1 x2
+            x1 <= x && x <= x2
+        )
+
+    [<Test>]
+    let ``IntervalSet add works`` () =
+        let property (pos : int ref) (neg : int ref) (x : int) (xs : (int * int) list) =
+            let intervals = toIntervalSet xs
+
+            let actual = IntervalSet.contains x intervals
+            let expected = modelContains x xs
+
+            if actual then
+                Interlocked.Increment pos |> ignore
+            else
+                Interlocked.Increment neg |> ignore
+
+            expected = actual
+
+        let pos = ref 0
+        let neg = ref 0
+
+        Check.One (
+            { Config.Default with
+                MaxTest = 1000
+            },
+            property pos neg
+        )
+
+        printfn "Fraction of positive cases: %f" ((float pos.Value) / (float pos.Value + float neg.Value))
+
+    [<Test>]
+    let ``Intersection works`` () =
+        let property
+            (pos : int ref)
+            (neg : int ref)
+            (trials : int list)
+            (xsModel : (int * int) list)
+            (ysModel : (int * int) list)
+            =
+            let xs = toIntervalSet xsModel
+            let ys = toIntervalSet ysModel
+
+            let intervals = IntervalSet.intersection xs ys
+
+            for x in trials do
+                let actual = IntervalSet.contains x intervals
+                let expected = modelContains x xsModel && modelContains x ysModel
+
+                expected |> shouldEqual actual
+
+                if actual then
+                    Interlocked.Increment pos |> ignore
+                else
+                    Interlocked.Increment neg |> ignore
+
+        let pos = ref 0
+        let neg = ref 0
+
+        Check.One (
+            { Config.Default with
+                MaxTest = 1000
+            },
+            property pos neg
+        )
+
+        printfn "Fraction of positive cases: %f" ((float pos.Value) / (float pos.Value + float neg.Value))

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/day19.txt

@@ -0,0 +1,17 @@
+px{a<2006:qkq,m>2090:A,rfg}
+pv{a>1716:R,A}
+lnx{m>1548:A,A}
+rfg{s<537:gd,x>2440:R,A}
+qs{s>3448:A,lnx}
+qkq{x<1416:A,crn}
+crn{x>2662:A,R}
+in{s<1351:px,qqz}
+qqz{s>2770:qs,m<1801:hdj,R}
+gd{a>3333:R,R}
+hdj{m>838:A,pv}
+
+{x=787,m=2655,a=1222,s=2876}
+{x=1679,m=44,a=2067,s=496}
+{x=2036,m=264,a=79,s=2244}
+{x=2461,m=1339,a=466,s=291}
+{x=2127,m=1623,a=2188,s=1013}

mathematica/day_21.m

@@ -0,0 +1,30 @@
+(* ::Package:: *)
+
+(* ::Input:: *)
+(*s="...........*)
+(*.....###.#.*)
+(*.###.##..#.*)
+(*..#.#...#..*)
+(*....#.#....*)
+(*.##..S####.*)
+(*.##..#...#.*)
+(*.......##..*)
+(*.##.#.####.*)
+(*.##..##.##.*)
+(*...........";*)
+
+
+(* ::Input:: *)
+(*reachable[grid_,{row_Integer,col_Integer}]:=reachable[grid,{row,col}]=Select[{{row+1,col},{row-1,col},{row,col+1},{row,col-1}},*)
+(*1<=#[[1]]<=Length[grid]&&1<=#[[2]]<=Length[First@grid]&&grid[[#[[1]],#[[2]]]]!="#"&*)
+(*]*)
+
+
+(* ::Input:: *)
+(*f[grid_,pos_,0]:={pos}*)
+(*f[grid_,pos_,timestepsRemaining_Integer]:=*)
+(*f[grid,pos,timestepsRemaining]=DeleteDuplicates@Flatten[f[grid,#,timestepsRemaining-1]&/@reachable[grid,pos],1]*)
+
+
+(* ::Input:: *)
+(*With[{grid=Characters/@StringSplit[s,"\n"]},f[grid,FirstPosition[grid,"S"],64]//Length]*)