diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj
index 10eaced..7c5ca68 100644
--- a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj
@@ -21,6 +21,7 @@
     <Compile Include="Day8.fs"/>
     <Compile Include="Day9.fs"/>
     <Compile Include="Day10.fs" />
+    <Compile Include="Day11.fs" />
   </ItemGroup>
 
 </Project>
diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day11.fs b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day11.fs
new file mode 100644
index 0000000..6c8c4d6
--- /dev/null
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day11.fs
@@ -0,0 +1,81 @@
+namespace AdventOfCode2023
+
+open System
+
+[<RequireQualifiedAccess>]
+module Day11 =
+
+    let inline private toRowAndCol (lineLength : int) (pos : int) : struct (int * int) =
+        let lineNum = pos / lineLength
+        let withinLine = pos % lineLength
+        struct (lineNum, withinLine)
+
+    let inline private ofRowAndCol (lineLength : int) (lineNum : int) (col : int) : int = lineNum * lineLength + col
+
+    let part1 (s : string) =
+        let galaxies = ResizeArray ()
+        let rowsWithoutGalaxies = ResizeArray ()
+        let rowLength = s.IndexOf '\n'
+        let mutable hasAnyGalaxy = false
+        let mutable currRowIndex = 0
+        let mutable currColIndex = 0
+
+        for c in s do
+            if c = '\n' then
+                if not hasAnyGalaxy then
+                    rowsWithoutGalaxies.Add currRowIndex
+
+                currRowIndex <- currRowIndex + 1
+                currColIndex <- 0
+                hasAnyGalaxy <- false
+            elif c = '#' then
+                hasAnyGalaxy <- true
+                galaxies.Add (currRowIndex, currColIndex)
+                currColIndex <- currColIndex + 1
+            else
+                currColIndex <- currColIndex + 1
+
+        galaxies.Sort (fun (_, c1) (_, c2) -> compare c1 c2)
+
+        let colsWithoutGalaxies =
+            let result = ResizeArray ()
+            let mutable prevCol = 0
+
+            for (_, c) in galaxies do
+                if c > prevCol then
+                    for j = prevCol + 1 to c - 1 do
+                        result.Add j
+
+                    prevCol <- c
+
+            result
+
+        let mutable answer = 0
+
+        for galaxy1 = 0 to galaxies.Count - 1 do
+            let row1, col1 = galaxies.[galaxy1]
+
+            for galaxy2 = galaxy1 + 1 to galaxies.Count - 1 do
+                let row2, col2 = galaxies.[galaxy2]
+                let baseDistance = abs (row1 - row2) + abs (col1 - col2)
+
+                let extraDistance =
+                    let mutable extraDistance = 0
+
+                    for i = 1 + min row1 row2 to max row1 row2 - 1 do
+                        if rowsWithoutGalaxies.Contains i then
+                            extraDistance <- extraDistance + 1
+
+                    for i = 1 + min col1 col2 to max col1 col2 - 1 do
+                        if colsWithoutGalaxies.Contains i then
+                            extraDistance <- extraDistance + 1
+
+                    extraDistance
+
+                answer <- answer + extraDistance + baseDistance
+
+        answer
+
+    let part2 (s : string) =
+        use s = StringSplitEnumerator.make '\n' s
+        0
diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs
index 3343dae..218bd1d 100644
--- a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs
@@ -211,6 +211,22 @@ module Program =
             Console.WriteLine (part2.ToString ())
             Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
 
+        Console.WriteLine "=====Day 11====="
+
+        do
+            let input = Path.Combine (dir.FullName, "day11.txt") |> File.ReadAllText
+
+            sw.Restart ()
+            let part1 = Day11.part1 input
+            sw.Stop ()
+            Console.WriteLine (part1.ToString ())
+            Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
+            sw.Restart ()
+            let part2 = Day11.part2 input
+            sw.Stop ()
+            Console.WriteLine (part2.ToString ())
+            Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
+
         endToEnd.Stop ()
 
         Console.Error.WriteLine (
diff --git a/AdventOfCode2023.FSharp/Test/Test.fsproj b/AdventOfCode2023.FSharp/Test/Test.fsproj
index b511fbe..9fe6516 100644
--- a/AdventOfCode2023.FSharp/Test/Test.fsproj
+++ b/AdventOfCode2023.FSharp/Test/Test.fsproj
@@ -19,6 +19,7 @@
     <Compile Include="TestDay8.fs"/>
     <Compile Include="TestDay9.fs"/>
     <Compile Include="TestDay10.fs" />
+    <Compile Include="TestDay11.fs" />
     <EmbeddedResource Include="samples\day1.txt"/>
     <EmbeddedResource Include="samples\day1part1.txt"/>
     <EmbeddedResource Include="samples\day2.txt"/>
@@ -32,6 +33,7 @@
     <EmbeddedResource Include="samples\day9.txt"/>
     <EmbeddedResource Include="samples\day10part1.txt" />
     <EmbeddedResource Include="samples\day10.txt" />
+    <EmbeddedResource Include="samples\day11.txt" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/AdventOfCode2023.FSharp/Test/TestDay11.fs b/AdventOfCode2023.FSharp/Test/TestDay11.fs
new file mode 100644
index 0000000..ffc65c6
--- /dev/null
+++ b/AdventOfCode2023.FSharp/Test/TestDay11.fs
@@ -0,0 +1,44 @@
+namespace AdventOfCode2023.Test
+
+open AdventOfCode2023
+open NUnit.Framework
+open FsUnitTyped
+open System.IO
+
+[<TestFixture>]
+module TestDay11 =
+
+    let sample = Assembly.getEmbeddedResource typeof<Dummy>.Assembly "day11.txt"
+
+    [<Test>]
+    let part1Sample () =
+        sample |> Day11.part1 |> shouldEqual 374
+
+    [<Test>]
+    let part2Sample () = sample |> Day11.part2 |> shouldEqual -1
+
+    [<Test>]
+    let part1Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day11.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day11.part1 s |> shouldEqual 9947476
+
+    [<Test>]
+    let part2Actual () =
+        let s =
+            try
+                File.ReadAllText (Path.Combine (__SOURCE_DIRECTORY__, "../../inputs/day11.txt"))
+            with
+            | :? DirectoryNotFoundException
+            | :? FileNotFoundException ->
+                Assert.Inconclusive ()
+                failwith "unreachable"
+
+        Day11.part2 s |> shouldEqual -1
diff --git a/AdventOfCode2023.FSharp/Test/TestDay9.fs b/AdventOfCode2023.FSharp/Test/TestDay9.fs
index 6d9c969..38b4822 100644
--- a/AdventOfCode2023.FSharp/Test/TestDay9.fs
+++ b/AdventOfCode2023.FSharp/Test/TestDay9.fs
@@ -15,10 +15,7 @@ module TestDay9 =
         sample |> Day9.part1 |> shouldEqual 114L
 
     [<Test>]
-    let part2Sample () =
-        Assembly.getEmbeddedResource typeof<Dummy>.Assembly "day9.txt"
-        |> Day9.part2
-        |> shouldEqual 2L
+    let part2Sample () = sample |> Day9.part2 |> shouldEqual 2L
 
     [<Test>]
     let part1Actual () =
diff --git a/AdventOfCode2023.FSharp/Test/samples/day11.txt b/AdventOfCode2023.FSharp/Test/samples/day11.txt
new file mode 100644
index 0000000..986aad4
--- /dev/null
+++ b/AdventOfCode2023.FSharp/Test/samples/day11.txt
@@ -0,0 +1,10 @@
+...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....