Add satellite exercise

config.json

@@ -2233,6 +2233,20 @@
           "result"
         ],
         "difficulty": 5
+      },
+      {
+        "slug": "satellite",
+        "name": "Satellite",
+        "uuid": "bcfeb5b7-08d3-4039-95b2-ebda6b7288aa",
+        "practices": [
+          "recursion"
+        ],
+        "prerequisites": [
+          "recursion",
+          "discriminated-unions",
+          "numbers"
+        ],
+        "difficulty": 7
       }
     ],
     "foregone": [

exercises/Exercises.sln

@@ -309,6 +309,8 @@ Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "KillerSudokuHelper", "pract
 EndProject
 Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "StateOfTicTacToe", "practice\state-of-tic-tac-toe\StateOfTicTacToe.fsproj", "{A12FEF19-5EE8-430E-BD66-2D93ADFC1944}"
 EndProject
+Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "Satellite", "practice\satellite\Satellite.fsproj", "{FF432193-3D08-4BD4-ADCD-1512BF67A425}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -910,6 +912,10 @@ Global
 		{A12FEF19-5EE8-430E-BD66-2D93ADFC1944}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A12FEF19-5EE8-430E-BD66-2D93ADFC1944}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A12FEF19-5EE8-430E-BD66-2D93ADFC1944}.Release|Any CPU.Build.0 = Release|Any CPU
+		{FF432193-3D08-4BD4-ADCD-1512BF67A425}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{FF432193-3D08-4BD4-ADCD-1512BF67A425}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{FF432193-3D08-4BD4-ADCD-1512BF67A425}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{FF432193-3D08-4BD4-ADCD-1512BF67A425}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{B404AA3C-A226-409A-A035-6C1DC66940DD} = {B7E719DB-FB8D-43B4-B529-55FCF6E3DC3F}
@@ -1063,5 +1069,6 @@ Global
 		{1850FAE9-5ACB-41D0-91BB-AD17A1021248} = {391BEEC4-91A8-43F3-AE94-D5CB9A8FA611}
 		{FCE9E627-CFF9-4EF3-84BE-D42B354825AA} = {391BEEC4-91A8-43F3-AE94-D5CB9A8FA611}
 		{A12FEF19-5EE8-430E-BD66-2D93ADFC1944} = {391BEEC4-91A8-43F3-AE94-D5CB9A8FA611}
+		{FF432193-3D08-4BD4-ADCD-1512BF67A425} = {391BEEC4-91A8-43F3-AE94-D5CB9A8FA611}
 	EndGlobalSection
 EndGlobal

exercises/practice/satellite/.config/dotnet-tools.json

@@ -0,0 +1,12 @@
+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "fantomas-tool": {
+      "version": "4.7.9",
+      "commands": [
+        "fantomas"
+      ]
+    }
+  }
+}

exercises/practice/satellite/.docs/instructions.md

@@ -0,0 +1,27 @@
+# Instructions
+
+Imagine you need to transmit a binary tree to a satellite approaching Alpha Centauri and you have limited bandwidth.
+Since the tree has no repeating items it can be uniquely represented by its [pre-order and in-order traversals][wiki].
+
+Write the software for the satellite to rebuild the tree from the traversals.
+
+A pre-order traversal reads the value of the current node before (hence "pre") reading the left subtree in pre-order.
+Afterwards the right subtree is read in pre-order.
+
+An in-order traversal reads the left subtree in-order then the current node and finally the right subtree in-order.
+So in order from left to right.
+
+For example the pre-order traversal of this tree is [a, i, x, f, r].
+The in-order traversal of this tree is [i, a, f, x, r]
+
+```text
+  a
+ / \
+i   x
+   / \
+  f   r
+```
+
+Note: the first item in the pre-order traversal is always the root.
+
+[wiki]: https://en.wikipedia.org/wiki/Tree_traversal

exercises/practice/satellite/.meta/Example.fs

@@ -0,0 +1,24 @@
+module Satellite
+
+type Tree =
+    | Empty
+    | Node of value: string * left: Tree * right: Tree
+
+let rec createTree inorder preorder =
+    match preorder with
+    | [] -> Empty
+    | hd :: tail ->
+        let hdIdx = inorder |> List.findIndex (fun x -> x = hd)
+        let leftInorder, rightInorder = inorder[0 .. hdIdx - 1], inorder[hdIdx + 1 ..]
+        let leftPreorder, rightPreorder = tail[0 .. leftInorder.Length - 1], tail[leftInorder.Length ..]
+        Node(hd, createTree leftInorder leftPreorder, createTree rightInorder rightPreorder)
+
+let treeFromTraversals preorder inorder =
+    if List.length preorder <> List.length inorder then
+        Error "traversals must have the same length"
+    elif List.sort preorder <> List.sort inorder then
+        Error "traversals must have the same elements"
+    elif List.distinct preorder <> preorder then
+        Error "traversals must contain unique items"
+    else
+        Ok(createTree preorder inorder)

exercises/practice/satellite/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "erikschierboom"
+  ],
+  "files": {
+    "solution": [
+      "Satellite.fs"
+    ],
+    "test": [
+      "SatelliteTests.fs"
+    ],
+    "example": [
+      ".meta/Example.fs"
+    ]
+  },
+  "blurb": "Rebuild binary trees from pre-order and in-order traversals."
+}

exercises/practice/satellite/.meta/tests.toml

@@ -0,0 +1,28 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[8df3fa26-811a-4165-9286-ff9ac0850d19]
+description = "Empty tree"
+
+[f945ccfc-05e3-47d7-825b-0270559d43ad]
+description = "Tree with one item"
+
+[a0121d5f-37b0-48dd-9c64-cba4c4464135]
+description = "Tree with many items"
+
+[6074041f-4891-4d81-a128-401050c2a3b0]
+description = "Reject traversals of different length"
+
+[27916ce4-45f3-4d8b-8528-496fedc157ca]
+description = "Reject inconsistent traversals of same length"
+
+[d86a3d72-76a9-43b5-9d3a-e64cb1216035]
+description = "Reject traversals with repeated items"

exercises/practice/satellite/Satellite.fs

@@ -0,0 +1,8 @@
+module Satellite
+
+type Tree =
+    | Empty
+    | Node of value: string * left: Tree * right: Tree
+
+let treeFromTraversals preorder inorder =
+    failwith "Please implement the 'treeFromTraversals' function"

exercises/practice/satellite/Satellite.fsproj

@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <IsPackable>false</IsPackable>
+    <GenerateProgramFile>false</GenerateProgramFile>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Satellite.fs" />
+    <Compile Include="SatelliteTests.fs" />
+  </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Exercism.Tests" Version="0.1.0-beta1" />
+    <PackageReference Include="FsUnit.xUnit" Version="4.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+</Project>

exercises/practice/satellite/SatelliteTests.fs

@@ -0,0 +1,51 @@
+module SatelliteTests
+
+open FsUnit.Xunit
+open Xunit
+
+open Satellite
+
+[<Fact>]
+let ``Empty tree`` () =
+    let expected: Result<Tree,string> = Ok (
+        Empty
+    )
+    treeFromTraversals [] [] |> should equal expected
+
+[<Fact>]
+let ``Tree with one item`` () =
+    let expected: Result<Tree,string> = Ok (
+        Node("a", Empty, Empty)
+    )
+    treeFromTraversals ["a"] ["a"] |> should equal expected
+
+[<Fact>]
+let ``Tree with many items`` () =
+    let expected: Result<Tree,string> = Ok (
+        Node(
+            "a",
+            Node("i", Empty, Empty),
+            Node(
+                "x",
+                Node("f", Empty, Empty),
+                Node("r", Empty, Empty)
+            )
+        )
+    )
+    treeFromTraversals ["i"; "a"; "f"; "x"; "r"] ["a"; "i"; "x"; "f"; "r"] |> should equal expected
+
+[<Fact>]
+let ``Reject traversals of different length`` () =
+    let expected: Result<Tree,string> = Error "traversals must have the same length"
+    treeFromTraversals ["b"; "a"; "r"] ["a"; "b"] |> should equal expected
+
+[<Fact>]
+let ``Reject inconsistent traversals of same length`` () =
+    let expected: Result<Tree,string> = Error "traversals must have the same elements"
+    treeFromTraversals ["a"; "b"; "c"] ["x"; "y"; "z"] |> should equal expected
+
+[<Fact>]
+let ``Reject traversals with repeated items`` () =
+    let expected: Result<Tree,string> = Error "traversals must contain unique items"
+    treeFromTraversals ["b"; "a"; "a"] ["a"; "b"; "a"] |> should equal expected
+

generators/Generators.fs

@@ -2056,3 +2056,37 @@ type KillerSudokuHelper() =
 
 type StateOfTicTacToe() =
     inherit ExerciseGenerator()
+
+type Satellite() =
+    inherit ExerciseGenerator()
+
+    let renderTree (root: JToken) =
+        let rec render indent (node: JToken)  =
+            let indentation = String(' ', indent * 4)
+
+            if node.HasValues then
+                let value = node["v"]
+                let left = node["l"] |> render (indent + 1)
+                let right = node["r"] |> render (indent + 1)
+
+                if node["l"].HasValues || node["r"].HasValues then
+                    $"{indentation}Node(\n" +
+                    $"{indentation}    \"{value}\",\n" +
+                    $"{left},\n" +
+                    $"{right}\n" +
+                    $"{indentation})"
+                else
+                    $"{indentation}Node(\"{value}\", Empty, Empty)"
+            else
+                $"{indentation}Empty"
+
+        render 2 root
+
+    override _.PropertiesWithIdentifier _ = [ "expected" ]
+
+    override _.IdentifierTypeAnnotation(_, _, _) = Some "Result<Tree,string>"
+
+    override _.RenderExpected(_, _, value) =
+        match value.SelectToken "error" with
+        | null -> $"Ok (\n%s{renderTree value}\n    )"
+        | error -> $"Error \"%s{string error}\""