AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day12.fs

@@ -8,11 +8,12 @@ open System.Globalization
 module Day12 =
 
     let rec solve
-        (dict : Dictionary<int * int, 'a>)
+        (dict : Dictionary<int * int, uint64>)
         (line : ReadOnlySpan<char>)
         (groups : IReadOnlyList<int>)
+        (remainingToFill : int)
         (currentGroupIndex : int)
-        : 'a
+        : uint64
         =
         if line.Length = 0 then
             if currentGroupIndex = groups.Count then
@@ -30,15 +31,7 @@ module Day12 =
         | true, v -> v
         | false, _ ->
 
-        let remaining =
-            let mutable remaining = -1
-
-            for i = currentGroupIndex to groups.Count - 1 do
-                remaining <- remaining + groups.[i] + 1
-
-            remaining
-
-        if remaining > line.Length then
+        if remainingToFill > line.Length then
             dict.Add ((line.Length, currentGroupIndex), LanguagePrimitives.GenericZero)
             LanguagePrimitives.GenericZero
         else
@@ -60,10 +53,20 @@ module Day12 =
                     if line.[groups.[currentGroupIndex]] = '#' then
                         LanguagePrimitives.GenericZero
                     else
-                        solve dict (line.Slice (groups.[currentGroupIndex] + 1)) groups (currentGroupIndex + 1)
+                        solve
+                            dict
+                            (line.Slice (groups.[currentGroupIndex] + 1))
+                            groups
+                            (remainingToFill - groups.[currentGroupIndex] - 1)
+                            (currentGroupIndex + 1)
                 else
-                    solve dict ReadOnlySpan<_>.Empty groups (currentGroupIndex + 1)
-        | '.' -> solve dict (line.Slice 1) groups currentGroupIndex
+                    solve
+                        dict
+                        ReadOnlySpan<_>.Empty
+                        groups
+                        (remainingToFill - groups.[currentGroupIndex] - 1)
+                        (currentGroupIndex + 1)
+        | '.' -> solve dict (line.Slice 1) groups remainingToFill currentGroupIndex
         | '?' ->
             let afterMark = line.IndexOfAnyExcept ('?', '#')
 
@@ -75,10 +78,10 @@ module Day12 =
                     // this group *is* filled in, contradiction
                     LanguagePrimitives.GenericZero
                 else
-                    solve dict (line.Slice afterMark) groups currentGroupIndex
+                    solve dict (line.Slice afterMark) groups remainingToFill currentGroupIndex
             else
 
-            let ifDot = solve dict (line.Slice 1) groups currentGroupIndex
+            let ifDot = solve dict (line.Slice 1) groups remainingToFill currentGroupIndex
             dict.TryAdd ((line.Length - 1, currentGroupIndex), ifDot) |> ignore
 
             let ifHash =
@@ -100,9 +103,19 @@ module Day12 =
                         then
                             LanguagePrimitives.GenericZero
                         else
-                            solve dict (line.Slice (groups.[currentGroupIndex] + 1)) groups (currentGroupIndex + 1)
+                            solve
+                                dict
+                                (line.Slice (groups.[currentGroupIndex] + 1))
+                                groups
+                                (remainingToFill - groups.[currentGroupIndex] - 1)
+                                (currentGroupIndex + 1)
                     else
-                        solve dict ReadOnlySpan<_>.Empty groups (currentGroupIndex + 1)
+                        solve
+                            dict
+                            ReadOnlySpan<_>.Empty
+                            groups
+                            (remainingToFill - groups.[currentGroupIndex] - 1)
+                            (currentGroupIndex + 1)
 
             ifDot + ifHash
         | _ ->
@@ -117,6 +130,8 @@ module Day12 =
         let mutable answer = 0uL
         let arr = ResizeArray ()
 
+        let dict = Dictionary ()
+
         for line in lines do
             if not line.IsEmpty then
                 arr.Clear ()
@@ -125,7 +140,16 @@ module Day12 =
                 for int in ints do
                     arr.Add (Int32.Parse (int, NumberStyles.None, CultureInfo.InvariantCulture))
 
-                let solved = solve (Dictionary ()) line arr 0
+                let remainingToFill =
+                    let mutable ans = -1
+
+                    for i = 0 to arr.Count - 1 do
+                        ans <- ans + arr.[i] + 1
+
+                    ans
+
+                dict.Clear ()
+                let solved = solve dict line arr remainingToFill 0
                 answer <- answer + solved
 
         answer
@@ -136,6 +160,8 @@ module Day12 =
         let mutable answer = 0uL
         let arr = ResizeArray ()
 
+        let dict = Dictionary ()
+
         for line in lines do
             if not line.IsEmpty then
                 arr.Clear ()
@@ -152,8 +178,16 @@ module Day12 =
                 let line =
                     String.Concat (sliced, '?', sliced, '?', sliced, '?', sliced, '?', sliced)
 
-                let solved = solve (Dictionary ()) (line.AsSpan ()) arr 0
-                printfn $"%s{line} : %i{solved}"
+                let remainingToFill =
+                    let mutable ans = -1
+
+                    for i = 0 to arr.Count - 1 do
+                        ans <- ans + arr.[i] + 1
+
+                    ans
+
+                dict.Clear ()
+                let solved = solve dict (line.AsSpan ()) arr remainingToFill 0
                 answer <- answer + solved
 
         answer

AdventOfCode2023.FSharp/Test/TestDay12.fs

@@ -42,4 +42,4 @@ module TestDay12 =
                 Assert.Inconclusive ()
                 failwith "unreachable"
 
-        Day12.part2 s |> shouldEqual 0uL
+        Day12.part2 s |> shouldEqual 3384337640277uL