Day 9 (#10)

AdventOfCode2022.App/AdventOfCode2022.App.fsproj

@@ -15,6 +15,7 @@
       <EmbeddedResource Include="..\AdventOfCode2022.Test\Inputs\Day6.txt" />
       <EmbeddedResource Include="..\AdventOfCode2022.Test\Inputs\Day7.txt" />
       <EmbeddedResource Include="..\AdventOfCode2022.Test\Inputs\Day8.txt" />
+      <EmbeddedResource Include="..\AdventOfCode2022.Test\Inputs\Day9.txt" />
     </ItemGroup>
 
     <ItemGroup>

AdventOfCode2022.App/Program.fs

@@ -13,14 +13,14 @@ module Program =
     let readResource (name : string) : string =
         let asm = Assembly.GetAssembly typeof<Dummy>
 
-        use stream = asm.GetManifestResourceStream (sprintf "AdventOfCode2022.App.%s" name)
+        use stream = asm.GetManifestResourceStream $"AdventOfCode2022.App.%s{name}"
 
         use reader = new StreamReader (stream)
         reader.ReadToEnd ()
 
     [<EntryPoint>]
     let main _ =
-        let days = Array.init 8 (fun day -> readResource $"Day%i{day + 1}.txt")
+        let days = Array.init 9 (fun day -> readResource $"Day%i{day + 1}.txt")
 
         let inline day (i : int) = days.[i - 1]
 
@@ -68,6 +68,11 @@ module Program =
             printfn "%i" (Day8.part1 day8)
             printfn "%i" (Day8.part2 day8)
 
+        do
+            let day9 = StringSplitEnumerator.make '\n' (day 9)
+            printfn "%i" (Day9.part1 day9)
+            printfn "%i" (Day9.part2 day9)
+
         time.Stop ()
         printfn $"Took %i{time.ElapsedMilliseconds}ms"
         0

AdventOfCode2022.Test/AdventOfCode2022.Test.fsproj

@@ -16,6 +16,7 @@
         <Compile Include="Day6.fs" />
         <Compile Include="Day7.fs" />
         <Compile Include="Day8.fs" />
+        <Compile Include="Day9.fs" />
         <EmbeddedResource Include="Inputs\Day1.txt" />
         <EmbeddedResource Include="Inputs\Day2.txt" />
         <EmbeddedResource Include="Inputs\Day3.txt" />
@@ -24,6 +25,7 @@
         <EmbeddedResource Include="Inputs\Day6.txt" />
         <EmbeddedResource Include="Inputs\Day7.txt" />
         <EmbeddedResource Include="Inputs\Day8.txt" />
+        <EmbeddedResource Include="Inputs\Day9.txt" />
     </ItemGroup>
 
     <ItemGroup>

AdventOfCode2022.Test/Day9.fs

@@ -0,0 +1,54 @@
+namespace AdventOfCode2022.Test
+
+open System
+open NUnit.Framework
+open FsUnitTyped
+open AdventOfCode2022
+
+[<TestFixture>]
+module TestDay9 =
+
+    let input =
+        """R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2
+"""
+
+    [<Test>]
+    let ``Part 1, given`` () =
+        Day9.part1 (StringSplitEnumerator.make '\n' input) |> shouldEqual 13
+
+    [<Test>]
+    let ``Part 1`` () =
+        let input = Assembly.readResource "Day9.txt"
+
+        Day9.part1 (StringSplitEnumerator.make '\n' input) |> shouldEqual 6023
+
+    [<Test>]
+    let ``Part 2, given 1`` () =
+        Day9.part2 (StringSplitEnumerator.make '\n' input) |> shouldEqual 1
+
+    let example2 =
+        """R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20
+"""
+
+    [<Test>]
+    let ``Part 2, given 2`` () =
+        Day9.part2 (StringSplitEnumerator.make '\n' example2) |> shouldEqual 36
+
+    [<Test>]
+    let ``Part 2`` () =
+        let input = Assembly.readResource "Day9.txt"
+        Day9.part2 (StringSplitEnumerator.make '\n' input) |> shouldEqual 2533

AdventOfCode2022/AdventOfCode2022.fsproj

@@ -17,6 +17,7 @@
       <Compile Include="Day6.fs" />
       <Compile Include="Day7.fs" />
       <Compile Include="Day8.fs" />
+      <Compile Include="Day9.fs" />
     </ItemGroup>
 
 </Project>

AdventOfCode2022/Day9.fs

@@ -0,0 +1,97 @@
+namespace AdventOfCode2022
+
+open System.Collections.Generic
+open System
+
+type Direction =
+    | Up
+    | Down
+    | Left
+    | Right
+
+[<RequireQualifiedAccess>]
+module Day9 =
+
+    let parse (lines : StringSplitEnumerator) : (Direction * int) IReadOnlyList =
+        use mutable enum = lines
+        let output = ResizeArray ()
+
+        for line in enum do
+            let line = line.TrimEnd ()
+
+            if not (line.IsWhiteSpace ()) then
+                let dir =
+                    match Char.ToUpperInvariant line.[0] with
+                    | 'U' -> Direction.Up
+                    | 'D' -> Direction.Down
+                    | 'L' -> Direction.Left
+                    | 'R' -> Direction.Right
+                    | _ -> failwith "Unexpected direction"
+
+                let distance = Int32.Parse (line.Slice 2)
+
+                output.Add (dir, distance)
+
+        output :> _
+
+    type Position = int * int
+
+    let bringTailTogether (head : Position) (tail : Position) : Position =
+        if abs (fst head - fst tail) <= 1 && abs (snd head - snd tail) <= 1 then
+            tail
+        elif fst head = fst tail then
+            fst head, snd head + (if snd head < snd tail then 1 else -1)
+        elif snd head = snd tail then
+            fst head + (if fst head < fst tail then 1 else -1), snd head
+        else
+            let fstCoord =
+                if abs (fst head - fst tail + 1) <= 1 then
+                    fst tail - 1
+                else
+                    fst tail + 1
+
+            let sndCoord =
+                if abs (snd head - snd tail + 1) <= 1 then
+                    snd tail - 1
+                else
+                    snd tail + 1
+
+            (fstCoord, sndCoord)
+
+    let newHead (pos : Position) (direction : Direction) : int * int =
+        match direction with
+        | Direction.Up -> fst pos, snd pos + 1
+        | Direction.Down -> fst pos, snd pos - 1
+        | Direction.Left -> fst pos - 1, snd pos
+        | Direction.Right -> fst pos + 1, snd pos
+
+    let go (count : int) (directions : (Direction * int) seq) : int =
+        let knots = Array.create count (0, 0)
+        let tailVisits = HashSet ()
+        tailVisits.Add (0, 0) |> ignore
+
+        for direction, distance in directions do
+            for _ in 1..distance do
+                let newHead = newHead knots.[0] direction
+                knots.[0] <- newHead
+
+                for knot in 1 .. knots.Length - 2 do
+                    knots.[knot] <- bringTailTogether knots.[knot - 1] knots.[knot]
+
+                let newTail = bringTailTogether knots.[knots.Length - 2] knots.[knots.Length - 1]
+
+                if newTail <> knots.[knots.Length - 1] then
+                    knots.[knots.Length - 1] <- newTail
+                    tailVisits.Add newTail |> ignore
+
+        tailVisits.Count
+
+    let part1 (lines : StringSplitEnumerator) : int =
+        let directions = parse lines
+
+        go 2 directions
+
+    let part2 (lines : StringSplitEnumerator) : int =
+        let directions = parse lines
+
+        go 10 directions