Part 1

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

@@ -1,12 +1,57 @@
 namespace AdventOfCode2023
 
+open System
+open System.Collections.Generic
+open System.Globalization
+
 [<RequireQualifiedAccess>]
 module Day12 =
 
+    let rec solve (line : ReadOnlySpan<char>) (groups : IReadOnlyList<int>) (currentGroupIndex : int) =
+        match line.[0] with
+        | '#' ->
+            if currentGroupIndex >= groups.Count then 0 else
+            let mutable isOk = true
+            for i = 1 to groups.[currentGroupIndex] - 1 do
+                if isOk && line.[i] <> '#' && line.[i] <> '?' then
+                    isOk <- false
+            if not isOk then 0 else
+            if line.[groups.[currentGroupIndex]] = '#' then 0 else
+            solve (line.Slice (groups.[currentGroupIndex] + 1)) groups (currentGroupIndex + 1)
+        | '.' ->
+            solve (line.Slice 1) groups currentGroupIndex
+        | '?' ->
+            let ifDot = solve (line.Slice 1) groups currentGroupIndex
+            let ifHash =
+                if currentGroupIndex >= groups.Count then 0 else
+                let mutable isOk = true
+                for i = 1 to groups.[currentGroupIndex] - 1 do
+                    if isOk && line.[i] <> '#' && line.[i] <> '?' then
+                        isOk <- false
+                if not isOk then 0 else
+                if line.[groups.[currentGroupIndex]] = '#' then 0 else
+                solve (line.Slice (groups.[currentGroupIndex] + 1)) groups (currentGroupIndex + 1)
+            ifDot + ifHash
+        | _ ->
+            if currentGroupIndex = groups.Count then 1 else 0
+
+
     let part1 (s : string) =
         use mutable lines = StringSplitEnumerator.make '\n' s
 
-        -1
+        let mutable answer = 0
+        let arr = ResizeArray ()
+        for line in lines do
+            if not line.IsEmpty then
+                arr.Clear ()
+                use ints = StringSplitEnumerator.make' ',' (line.Slice (line.IndexOf ' ' + 1))
+                for int in ints do
+                    arr.Add (Int32.Parse (int, NumberStyles.None, CultureInfo.InvariantCulture))
+
+                let solved = solve line arr 0
+                answer <- answer + solved
+
+        answer
 
     let part2 (s : string) =
         use mutable lines = StringSplitEnumerator.make '\n' s

AdventOfCode2023.FSharp/Test/TestDay12.fs

@@ -12,7 +12,7 @@ module TestDay12 =
 
     [<Test>]
     let part1Sample () =
-        sample |> Day12.part1 |> shouldEqual 0
+        sample |> Day12.part1 |> shouldEqual 21
 
     [<Test>]
     let part2Sample () =
@@ -31,7 +31,7 @@ module TestDay12 =
                 Assert.Inconclusive ()
                 failwith "unreachable"
 
-        Day12.part1 s |> shouldEqual 0
+        Day12.part1 s |> shouldEqual 7402
 
     [<Test>]
     let part2Actual () =

AdventOfCode2023.FSharp/Test/samples/day12.txt

@@ -0,0 +1,6 @@
+???.### 1,1,3
+.??..??...?##. 1,1,3
+?#?#?#?#?#?#?#? 1,3,1,6
+????.#...#... 4,1,1
+????.######..#####. 1,6,5
+?###???????? 3,2,1