[gleam] complete satellite

gleam/satellite/.gitignore

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+*.beam
+*.ez
+build
+erl_crash.dump

gleam/satellite/HELP.md

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+# Help
+
+## Running the tests
+
+To run the tests, run the command `gleam test` from within the exercise directory.
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit src/satellite.gleam` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Gleam track's documentation](https://exercism.org/docs/tracks/gleam)
+- The [Gleam track's programming category on the forum](https://forum.exercism.org/c/programming/gleam)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+To get help if you're having trouble, you can use one of the following resources:
+
+- [gleam.run](https://gleam.run/documentation/) is the gleam official documentation.
+- [Discord](https://discord.gg/Fm8Pwmy) is the discord channel.
+- [StackOverflow](https://stackoverflow.com/questions/tagged/gleam) can be used to search for your problem and see if it has been answered already. You can also ask and answer questions.

gleam/satellite/README.md

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+# Satellite
+
+Welcome to Satellite on Exercism's Gleam Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## 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
+
+## Source
+
+### Created by
+
+- @jiegillet

gleam/satellite/gleam.toml

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+name = "satellite"
+version = "0.1.0"
+
+[dependencies]
+gleam_bitwise = "~> 1.2"
+gleam_otp = "~> 0.7 or ~> 1.0"
+gleam_stdlib = "~> 0.32 or ~> 1.0"
+simplifile = "~> 1.0"
+gleam_erlang = ">= 0.25.0 and < 1.0.0"
+
+[dev-dependencies]
+exercism_test_runner = "~> 1.4"

gleam/satellite/manifest.toml

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+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "argv", version = "1.0.2", build_tools = ["gleam"], requirements = [], otp_app = "argv", source = "hex", outer_checksum = "BA1FF0929525DEBA1CE67256E5ADF77A7CDDFE729E3E3F57A5BDCAA031DED09D" },
+  { name = "exercism_test_runner", version = "1.8.0", build_tools = ["gleam"], requirements = ["argv", "gap", "glance", "gleam_community_ansi", "gleam_erlang", "gleam_json", "gleam_stdlib", "simplifile"], otp_app = "exercism_test_runner", source = "hex", outer_checksum = "B944D89A9D049897DF28C63D595D89CB54D8C407D06EFFCE4CDA8C3EC1C9F51E" },
+  { name = "filepath", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "EFB6FF65C98B2A16378ABC3EE2B14124168C0CE5201553DE652E2644DCFDB594" },
+  { name = "gap", version = "1.1.3", build_tools = ["gleam"], requirements = ["gleam_community_ansi", "gleam_stdlib"], otp_app = "gap", source = "hex", outer_checksum = "6EF5E3B523FDFBC317E9EA28D5163EE04744A97C007106F90207569789612291" },
+  { name = "glance", version = "0.11.0", build_tools = ["gleam"], requirements = ["gleam_stdlib", "glexer"], otp_app = "glance", source = "hex", outer_checksum = "8F3314D27773B7C3B9FB58D8C02C634290422CE531988C0394FA0DF8676B964D" },
+  { name = "gleam_bitwise", version = "1.3.1", build_tools = ["gleam"], requirements = [], otp_app = "gleam_bitwise", source = "hex", outer_checksum = "B36E1D3188D7F594C7FD4F43D0D2CE17561DE896202017548578B16FE1FE9EFC" },
+  { name = "gleam_community_ansi", version = "1.4.1", build_tools = ["gleam"], requirements = ["gleam_community_colour", "gleam_stdlib"], otp_app = "gleam_community_ansi", source = "hex", outer_checksum = "4CD513FC62523053E62ED7BAC2F36136EC17D6A8942728250A9A00A15E340E4B" },
+  { name = "gleam_community_colour", version = "1.4.0", build_tools = ["gleam"], requirements = ["gleam_json", "gleam_stdlib"], otp_app = "gleam_community_colour", source = "hex", outer_checksum = "795964217EBEDB3DA656F5EB8F67D7AD22872EB95182042D3E7AFEF32D3FD2FE" },
+  { name = "gleam_erlang", version = "0.25.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "054D571A7092D2A9727B3E5D183B7507DAB0DA41556EC9133606F09C15497373" },
+  { name = "gleam_json", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib", "thoas"], otp_app = "gleam_json", source = "hex", outer_checksum = "9063D14D25406326C0255BDA0021541E797D8A7A12573D849462CAFED459F6EB" },
+  { name = "gleam_otp", version = "0.10.0", build_tools = ["gleam"], requirements = ["gleam_erlang", "gleam_stdlib"], otp_app = "gleam_otp", source = "hex", outer_checksum = "0B04FE915ACECE539B317F9652CAADBBC0F000184D586AAAF2D94C100945D72B" },
+  { name = "gleam_stdlib", version = "0.39.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "2D7DE885A6EA7F1D5015D1698920C9BAF7241102836CE0C3837A4F160128A9C4" },
+  { name = "glexer", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "glexer", source = "hex", outer_checksum = "BD477AD657C2B637FEF75F2405FAEFFA533F277A74EF1A5E17B55B1178C228FB" },
+  { name = "simplifile", version = "1.7.0", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib"], otp_app = "simplifile", source = "hex", outer_checksum = "1D5DFA3A2F9319EC85825F6ED88B8E449F381B0D55A62F5E61424E748E7DDEB0" },
+  { name = "thoas", version = "1.2.1", build_tools = ["rebar3"], requirements = [], otp_app = "thoas", source = "hex", outer_checksum = "E38697EDFFD6E91BD12CEA41B155115282630075C2A727E7A6B2947F5408B86A" },
+]
+
+[requirements]
+exercism_test_runner = { version = "~> 1.4" }
+gleam_bitwise = { version = "~> 1.2" }
+gleam_erlang = { version = ">= 0.25.0 and < 1.0.0" }
+gleam_otp = { version = "~> 0.7 or ~> 1.0" }
+gleam_stdlib = { version = "~> 0.32 or ~> 1.0" }
+simplifile = { version = "~> 1.0" }

gleam/satellite/src/satellite.gleam

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+import gleam/bool
+import gleam/list
+import gleam/set
+
+pub type Tree(a) {
+  Nil
+  Node(value: a, left: Tree(a), right: Tree(a))
+}
+
+pub type Error {
+  DifferentLengths
+  DifferentItems
+  NonUniqueItems
+}
+
+pub fn tree_from_traversals(
+  inorder inorder: List(a),
+  preorder preorder: List(a),
+) -> Result(Tree(a), Error) {
+  use <- bool.guard(
+    list.length(inorder) != list.length(preorder),
+    Error(DifferentLengths),
+  )
+
+  use <- bool.guard(
+    set.size(set.from_list(inorder)) != list.length(inorder),
+    Error(NonUniqueItems),
+  )
+
+  use <- bool.guard(
+    set.from_list(inorder) != set.from_list(preorder),
+    Error(DifferentItems),
+  )
+
+  Ok(traverse(inorder, preorder))
+}
+
+fn traverse(inorder: List(a), preorder: List(a)) -> Tree(a) {
+  use <- bool.guard(list.is_empty(inorder), Nil)
+
+  let assert Ok(root) = list.find(preorder, list.contains(inorder, _))
+  let assert #(left, [_, ..right]) =
+    list.split_while(inorder, fn(ch) { ch != root })
+
+  Node(root, traverse(left, preorder), traverse(right, preorder))
+}

gleam/satellite/test/satellite_test.gleam

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+import exercism/should
+import exercism/test_runner
+import satellite.{DifferentItems, DifferentLengths, Nil, Node, NonUniqueItems}
+
+pub fn main() {
+  test_runner.main()
+}
+
+pub fn empty_tree_test() {
+  satellite.tree_from_traversals(inorder: [], preorder: [])
+  |> should.equal(Ok(Nil))
+}
+
+pub fn tree_with_one_item_test() {
+  satellite.tree_from_traversals(inorder: ["a"], preorder: ["a"])
+  |> should.equal(Ok(Node(value: "a", left: Nil, right: Nil)))
+}
+
+pub fn tree_with_many_items_test() {
+  satellite.tree_from_traversals(inorder: ["i", "a", "f", "x", "r"], preorder: [
+    "a", "i", "x", "f", "r",
+  ])
+  |> should.equal(
+    Ok(Node(
+      value: "a",
+      left: Node(value: "i", left: Nil, right: Nil),
+      right: Node(
+        value: "x",
+        left: Node(value: "f", left: Nil, right: Nil),
+        right: Node(value: "r", left: Nil, right: Nil),
+      ),
+    )),
+  )
+}
+
+pub fn reject_traversals_of_different_length_test() {
+  satellite.tree_from_traversals(inorder: ["b", "a", "r"], preorder: ["a", "b"])
+  |> should.equal(Error(DifferentLengths))
+}
+
+pub fn reject_inconsistent_traversals_of_same_length_test() {
+  satellite.tree_from_traversals(inorder: ["a", "b", "c"], preorder: [
+    "x", "y", "z",
+  ])
+  |> should.equal(Error(DifferentItems))
+}
+
+pub fn reject_traversals_with_repeated_items_test() {
+  satellite.tree_from_traversals(inorder: ["b", "a", "a"], preorder: [
+    "a", "b", "a",
+  ])
+  |> should.equal(Error(NonUniqueItems))
+}