Speed up day 7 a bit (#7)

I'm going mad, why am I doing this

Co-authored-by: Smaug123 <patrick+github@patrickstevens.co.uk>
Reviewed-on: #7

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/ResizeArray.fs

@@ -0,0 +1,40 @@
+namespace AdventOfCode2023.ResizeArray
+
+open System
+
+type ResizeArray<'T> =
+    private
+        {
+            mutable Array : 'T array
+            mutable Length : int
+        }
+
+    member this.Count = this.Length
+    member this.Clear () = this.Length <- 0
+
+    member this.Add (t : 'T) =
+        if this.Length < this.Array.Length then
+            this.Array.[this.Length] <- t
+        else
+            let newLength = this.Length * 2
+            let newArray = Array.zeroCreate<'T> newLength
+            Array.blit this.Array 0 newArray 0 this.Length
+            newArray.[this.Length] <- t
+            this.Array <- newArray
+
+        this.Length <- this.Length + 1
+
+    member this.Item
+        with get (i : int) = this.Array.[i]
+        and set (i : int) (t : 'T) = this.Array.[i] <- t
+
+    member this.Sort () =
+        Span(this.Array).Slice(0, this.Count).Sort ()
+
+[<RequireQualifiedAccess>]
+module ResizeArray =
+    let create<'T> (capacity : int) =
+        {
+            Array = Array.zeroCreate<'T> capacity
+            Length = 0
+        }