Cleaner

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

@@ -13,6 +13,7 @@
         <Compile Include="Day3.fs" />
         <Compile Include="Day4.fs" />
         <Compile Include="Day5.fs" />
+        <Compile Include="Day6.fs" />
     </ItemGroup>
 
 </Project>

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day6.fs

@@ -0,0 +1,86 @@
+namespace AdventOfCode2023
+
+open System
+
+[<RequireQualifiedAccess>]
+module Day6 =
+
+    let parse (s : string) =
+        use mutable lines = StringSplitEnumerator.make '\n' s
+
+        let times =
+            lines.MoveNext () |> ignore
+            use mutable line = StringSplitEnumerator.make' ' ' lines.Current
+            StringSplitEnumerator.chomp "Time:" &line
+            line.MoveNext () |> ignore
+            let times = ResizeArray ()
+
+            while line.MoveNext () do
+                if not line.Current.IsEmpty then
+                    times.Add (UInt64.Parse line.Current)
+
+            times
+
+        let distance =
+            lines.MoveNext () |> ignore
+            use mutable line = StringSplitEnumerator.make' ' ' lines.Current
+            StringSplitEnumerator.chomp "Distance:" &line
+            line.MoveNext () |> ignore
+            let distance = ResizeArray ()
+
+            while line.MoveNext () do
+                if not line.Current.IsEmpty then
+                    distance.Add (UInt64.Parse line.Current)
+
+            distance
+
+        times, distance
+
+    let furthest (distance : uint64) (toBeat : uint64) =
+        // Count i in [1 .. distance - 1] such that (distance - i) * i > toBeat
+        // i.e. such that distance * i - i * i > toBeat
+        // -i^2 + distance * i - toBeat = 0 when:
+        // i = (distance +- sqrt(distance^2 - 4 * toBeat)) / 2
+        let distFloat = float distance
+        let inside = sqrt (distFloat * distFloat - 4.0 * float toBeat)
+        let limit1 = (distFloat + inside) / 2.0
+        let limit2 = (distFloat - sqrt (distFloat * distFloat - 4.0 * float toBeat)) / 2.0
+        // round limit2 up and limit1 down
+        let limit1 = uint64 (floor limit1)
+        let limit2 = uint64 (ceil limit2)
+        // cope with edge case of an exact square
+        if (uint64 inside) * (uint64 inside) = uint64 distance * uint64 distance - 4uL * uint64 toBeat then
+            limit1 - limit2 - 1uL
+        else
+            limit1 - limit2 + 1uL
+
+    let part1 (s : string) =
+        let times, distance = parse s
+        let mutable answer = 1uL
+
+        for i = 0 to times.Count - 1 do
+            let time = times.[i]
+            let distance = distance.[i]
+            let winners = furthest time distance
+            answer <- answer * winners
+
+        answer
+
+    let concat (digits : ResizeArray<uint64>) : uint64 =
+        let mutable answer = 0uL
+
+        for digit in digits do
+            let mutable power = 10uL
+
+            while digit >= power do
+                power <- power * 10uL
+
+            answer <- answer * power + digit
+
+        answer
+
+    let part2 (s : string) =
+        let times, distance = parse s
+        let concatTime = concat times
+        let concatDist = concat distance
+        furthest concatTime concatDist

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs

@@ -121,6 +121,21 @@ module Program =
             Console.WriteLine (part2.ToString ())
             Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
 
+        printfn "=====Day 6====="
+
+        do
+            let input = Path.Combine (dir.FullName, "day6.txt") |> File.ReadAllText
+            sw.Restart ()
+            let part1 = Day6.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 = Day6.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

@@ -14,12 +14,14 @@
         <Compile Include="TestDay3.fs" />
         <Compile Include="TestDay4.fs" />
         <Compile Include="TestDay5.fs" />
+        <Compile Include="TestDay6.fs" />
         <EmbeddedResource Include="samples\day1.txt" />
         <EmbeddedResource Include="samples\day1part1.txt" />
         <EmbeddedResource Include="samples\day2.txt" />
         <EmbeddedResource Include="samples\day3.txt" />
         <EmbeddedResource Include="samples\day4.txt" />
         <EmbeddedResource Include="samples\day5.txt" />
+        <EmbeddedResource Include="samples\day6.txt" />
     </ItemGroup>
 
     <ItemGroup>

AdventOfCode2023.FSharp/Test/TestDay6.fs

@@ -0,0 +1,46 @@
+namespace AdventOfCode2023.Test
+
+open System
+open AdventOfCode2023
+open NUnit.Framework
+open FsUnitTyped
+open System.IO
+
+[<TestFixture>]
+module TestDay6 =
+
+    let sample = Assembly.getEmbeddedResource typeof<Dummy>.Assembly "day6.txt"
+
+    [<Test>]
+    let part1Sample () =
+        sample |> Day6.part1 |> shouldEqual 288uL
+
+    [<Test>]
+    let part2Sample () =
+        sample |> Day6.part2 |> shouldEqual 71503uL
+
+    [<Test>]
+    let part1Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day6.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day6.part1 s |> shouldEqual 32076uL
+
+    [<Test>]
+    let part2Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day6.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day6.part2 s |> shouldEqual 34278221uL

AdventOfCode2023.FSharp/Test/samples/day6.txt

@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200