Tidy

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Bench/Inputs.fs

@@ -14,6 +14,6 @@ module Inputs =
             if isNull dir then
                 failwith "reached root of filesystem without finding inputs dir"
 
-        Array.init 12 (fun day -> Path.Combine (dir.FullName, "inputs", $"day%i{day + 1}.txt") |> File.ReadAllText)
+        Array.init 13 (fun day -> Path.Combine (dir.FullName, "inputs", $"day%i{day + 1}.txt") |> File.ReadAllText)
 
     let inline day (i : int) = days.[i - 1]

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Bench/Program.fs

@@ -44,7 +44,7 @@ module Benchmarks =
         [<GlobalSetup>]
         member _.Setup () = Run.shouldWrite <- false
 
-        [<Params(11, 12)>]
+        [<Params(11, 12, 13)>]
         member val Day = 0 with get, set
 
         [<Params(false, true)>]

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Bench/Run.fs

@@ -173,6 +173,18 @@ module Run =
             if shouldWrite then
                 Console.WriteLine output
 
+    let day13 (partTwo : bool) (input : string) =
+        if not partTwo then
+            let output = Day13.part1 input
+
+            if shouldWrite then
+                Console.WriteLine output
+        else
+            let output = Day13.part2 input
+
+            if shouldWrite then
+                Console.WriteLine output
+
     let allRuns =
         [|
             day1
@@ -187,4 +199,5 @@ module Run =
             day10
             day11
             day12
+            day13
         |]

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day13.fs

@@ -33,7 +33,7 @@ module Day13 =
 
         answer
 
-    let verifyHorizontalReflection (group : ResizeArray<'a>) (smaller : int) (bigger : int) : bool =
+    let verifyReflection (group : ResizeArray<'a>) (smaller : int) (bigger : int) : bool =
         let midPoint = (smaller + bigger) / 2
 
         let rec isOkWithin (curr : int) =
@@ -50,11 +50,12 @@ module Day13 =
 
         smaller = 0 || bigger = group.Count - 1
 
-    /// Find reflection among rows
+    /// Find reflection among rows.
+    /// Returns 0 to indicate "no answer".
     [<TailCall>]
-    let rec findRow (banAnswer : uint32) (rows : ResizeArray<uint32>) (currentLine : int) =
+    let rec findRow (banAnswer : uint32) (rows : ResizeArray<uint32>) (currentLine : int) : uint32 =
         if currentLine = rows.Count - 1 then
-            None
+            0ul
         else
             let mutable answer = UInt32.MaxValue
             let mutable i = currentLine
@@ -64,7 +65,7 @@ module Day13 =
 
                 if currentLine % 2 <> i % 2 then
                     if rows.[i] = rows.[currentLine] then
-                        if verifyHorizontalReflection rows currentLine i then
+                        if verifyReflection rows currentLine i then
                             let desiredAnswer = uint32 (((currentLine + i) / 2) + 1)
 
                             if desiredAnswer <> banAnswer then
@@ -72,7 +73,7 @@ module Day13 =
                                 i <- Int32.MaxValue
 
             if answer < UInt32.MaxValue then
-                Some answer
+                answer
             else
                 findRow banAnswer rows (currentLine + 1)
 
@@ -88,7 +89,8 @@ module Day13 =
             if not row.IsEmpty then
                 rowBuf.Add (rowToInt row)
 
-    let solve (banAnswer : uint32) (rowBuf : ResizeArray<_>) (colBuf : ResizeArray<_>) : uint32 option =
+    /// Returns 0 to indicate "no solution".
+    let solve (banAnswer : uint32) (rowBuf : ResizeArray<_>) (colBuf : ResizeArray<_>) : uint32 =
         match
             findRow
                 (if banAnswer >= 100ul then
@@ -98,8 +100,18 @@ module Day13 =
                 rowBuf
                 0
         with
-        | Some rowIndex -> Some (100ul * rowIndex)
-        | None -> findRow banAnswer colBuf 0
+        | rowIndex when rowIndex > 0ul -> 100ul * rowIndex
+        | _ -> findRow banAnswer colBuf 0
+
+    /// Returns also the group with this gro
+    let peelGroup (s : ReadOnlySpan<char>) : ReadOnlySpan<char> =
+        let index = s.IndexOf "\n\n"
+
+        if index < 0 then
+            // last group
+            s
+        else
+            s.Slice (0, index + 1)
 
     let part1 (s : string) =
         let mutable s = s.AsSpan ()
@@ -108,26 +120,20 @@ module Day13 =
         let mutable answer = 0ul
 
         while not s.IsEmpty do
-            let index = s.IndexOf "\n\n"
-
-            let group =
-                if index < 0 then
-                    // last group
-                    s
-                else
-                    s.Slice (0, index + 1)
+            let group = peelGroup s
 
             render rows cols group
-            answer <- answer + Option.get (solve UInt32.MaxValue rows cols)
+            // There's an obvious perf optimisation where we don't compute cols
+            // until we know there's no row answer. Life's too short.
+            answer <- answer + solve UInt32.MaxValue rows cols
 
-            if index < 0 then
+            if group.Length >= s.Length then
                 s <- ReadOnlySpan<char>.Empty
             else
-                s <- s.Slice (index + 2)
+                s <- s.Slice (group.Length + 1)
 
         answer
 
-    // 358 90 385 385 90 102 346
     let flipAt (rows : ResizeArray<_>) (cols : ResizeArray<_>) (rowNum : int) (colNum : int) : unit =
         rows.[rowNum] <-
             let index = 1ul <<< (cols.Count - colNum - 1)
@@ -152,18 +158,11 @@ module Day13 =
         let mutable answer = 0ul
 
         while not s.IsEmpty do
-            let index = s.IndexOf "\n\n"
-
-            let group =
-                if index < 0 then
-                    // last group
-                    s
-                else
-                    s.Slice (0, index + 1)
+            let group = peelGroup s
 
             render rows cols group
 
-            let bannedAnswer = solve UInt32.MaxValue rows cols |> Option.get
+            let bannedAnswer = solve UInt32.MaxValue rows cols
 
             let mutable isDone = false
             let mutable rowToChange = 0
@@ -175,7 +174,7 @@ module Day13 =
                     flipAt rows cols rowToChange colToChange
 
                     match solve bannedAnswer rows cols with
-                    | Some solved when solved > 0ul ->
+                    | solved when solved > 0ul ->
                         isDone <- true
                         answer <- answer + solved
                     | _ ->
@@ -184,9 +183,9 @@ module Day13 =
 
                 rowToChange <- rowToChange + 1
 
-            if index < 0 then
+            if group.Length >= s.Length then
                 s <- ReadOnlySpan<char>.Empty
             else
-                s <- s.Slice (index + 2)
+                s <- s.Slice (group.Length + 1)
 
         answer