binary_search_tree
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{
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"authors": [
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"sngeth"
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],
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"contributors": [
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"angelikatyborska",
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"Cohen-Carlisle",
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"devonestes",
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"neenjaw",
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"sotojuan"
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],
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"files": {
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"solution": [
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"lib/binary_search_tree.ex"
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],
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"test": [
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"test/binary_search_tree_test.exs"
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],
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"example": [
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".meta/example.ex"
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]
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},
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"blurb": "Insert and search for numbers in a binary tree.",
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"source": "Josh Cheek"
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}
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{"track":"elixir","exercise":"binary-search-tree","id":"fc6ed3ee9f82408eb78d0f9df5e506bf","url":"https://exercism.org/tracks/elixir/exercises/binary-search-tree","handle":"negrienko","is_requester":true,"auto_approve":false}
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# Used by "mix format"
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[
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inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
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]
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# The directory Mix will write compiled artifacts to.
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/_build/
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# If you run "mix test --cover", coverage assets end up here.
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/cover/
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# The directory Mix downloads your dependencies sources to.
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/deps/
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# Where third-party dependencies like ExDoc output generated docs.
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/doc/
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# Ignore .fetch files in case you like to edit your project deps locally.
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/.fetch
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# If the VM crashes, it generates a dump, let's ignore it too.
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erl_crash.dump
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# Also ignore archive artifacts (built via "mix archive.build").
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*.ez
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# Ignore package tarball (built via "mix hex.build").
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binary_search_tree-*.tar
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# Help
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## Running the tests
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From the terminal, change to the base directory of the exercise then execute the tests with:
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```bash
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$ mix test
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```
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This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
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Documentation:
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* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
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* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
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## Pending tests
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In test suites of practice exercises, all but the first test have been tagged to be skipped.
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Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
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For example:
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```elixir
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# @tag :pending
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test "shouting" do
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assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
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end
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```
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If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
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```bash
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$ mix test --include pending
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```
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Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
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```elixir
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# ExUnit.configure(exclude: :pending, trace: true)
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```
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## Useful `mix test` options
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* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
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* `--failed` - runs only tests that failed the last time they ran
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* `--max-failures` - the suite stops evaluating tests when this number of test failures
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is reached
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* `--seed 0` - disables randomization so the tests in a single file will always be ran
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in the same order they were defined in
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## Submitting your solution
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You can submit your solution using the `exercism submit lib/binary_search_tree.ex` command.
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This command will upload your solution to the Exercism website and print the solution page's URL.
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It's possible to submit an incomplete solution which allows you to:
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- See how others have completed the exercise
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- Request help from a mentor
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## Need to get help?
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If you'd like help solving the exercise, check the following pages:
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- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
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- The [Elixir track's programming category on the forum](https://forum.exercism.org/c/programming/elixir)
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- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
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- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
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Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
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If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.
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# Binary Search Tree
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Welcome to Binary Search Tree on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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## Instructions
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Insert and search for numbers in a binary tree.
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When we need to represent sorted data, an array does not make a good data structure.
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Say we have the array `[1, 3, 4, 5]`, and we add 2 to it so it becomes `[1, 3, 4, 5, 2]`.
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Now we must sort the entire array again!
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We can improve on this by realizing that we only need to make space for the new item `[1, nil, 3, 4, 5]`, and then adding the item in the space we added.
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But this still requires us to shift many elements down by one.
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Binary Search Trees, however, can operate on sorted data much more efficiently.
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A binary search tree consists of a series of connected nodes.
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Each node contains a piece of data (e.g. the number 3), a variable named `left`, and a variable named `right`.
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The `left` and `right` variables point at `nil`, or other nodes.
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Since these other nodes in turn have other nodes beneath them, we say that the left and right variables are pointing at subtrees.
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All data in the left subtree is less than or equal to the current node's data, and all data in the right subtree is greater than the current node's data.
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For example, if we had a node containing the data 4, and we added the data 2, our tree would look like this:
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4
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/
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2
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If we then added 6, it would look like this:
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4
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/ \
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2 6
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If we then added 3, it would look like this
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4
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/ \
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2 6
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\
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3
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And if we then added 1, 5, and 7, it would look like this
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4
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/ \
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/ \
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2 6
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/ \ / \
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1 3 5 7
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## Source
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### Created by
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- @sngeth
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### Contributed to by
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- @angelikatyborska
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- @Cohen-Carlisle
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- @devonestes
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- @neenjaw
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- @sotojuan
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### Based on
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Josh Cheek
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defmodule BinarySearchTree do
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@type bst_node :: %{data: any, left: bst_node | nil, right: bst_node | nil}
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@doc """
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Create a new Binary Search Tree with root's value as the given 'data'
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"""
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@spec new(any) :: bst_node
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def new(data), do: %{data: data, left: nil, right: nil}
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@doc """
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Creates and inserts a node with its value as 'data' into the tree.
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"""
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@spec insert(bst_node, any) :: bst_node
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def insert(nil, data), do: new(data)
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def insert(tree, data) when data <= tree.data, do:
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%{tree | left: insert(tree.left, data)}
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def insert(tree, data), do:
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%{tree | right: insert(tree.right, data)}
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@doc """
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Traverses the Binary Search Tree in order and returns a list of each node's data.
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"""
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@spec in_order(bst_node) :: [any]
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def in_order(nil), do: []
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def in_order(tree), do: in_order(tree.left) ++ [tree.data | in_order(tree.right)]
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end
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defmodule BinarySearchTree.MixProject do
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use Mix.Project
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def project do
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[
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app: :binary_search_tree,
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version: "0.1.0",
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# elixir: "~> 1.8",
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start_permanent: Mix.env() == :prod,
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deps: deps()
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]
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end
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# Run "mix help compile.app" to learn about applications.
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def application do
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[
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extra_applications: [:logger]
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]
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end
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# Run "mix help deps" to learn about dependencies.
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defp deps do
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[
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# {:dep_from_hexpm, "~> 0.3.0"},
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# {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
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]
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end
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end
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defmodule BinarySearchTreeTest do
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use ExUnit.Case
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test "data is retained" do
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root = BinarySearchTree.new(4)
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assert root.data == 4
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assert root.left == nil
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assert root.right == nil
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end
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describe "insert data at proper node" do
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test "smaller number at left node" do
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root =
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BinarySearchTree.new(4)
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|> BinarySearchTree.insert(2)
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assert root.data == 4
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assert root.left.data == 2
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assert root.left.left == nil
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assert root.left.right == nil
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assert root.right == nil
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end
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test "same number at left node" do
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root =
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BinarySearchTree.new(4)
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|> BinarySearchTree.insert(4)
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assert root.data == 4
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assert root.left.data == 4
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assert root.left.left == nil
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assert root.left.right == nil
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assert root.right == nil
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end
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test "greater number at right node" do
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root =
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BinarySearchTree.new(4)
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|> BinarySearchTree.insert(5)
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assert root.data == 4
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assert root.left == nil
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assert root.right.data == 5
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assert root.right.left == nil
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assert root.right.right == nil
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end
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end
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test "can create complex tree" do
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root =
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BinarySearchTree.new(4)
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|> BinarySearchTree.insert(2)
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|> BinarySearchTree.insert(6)
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|> BinarySearchTree.insert(1)
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|> BinarySearchTree.insert(3)
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|> BinarySearchTree.insert(5)
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|> BinarySearchTree.insert(7)
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assert root.data == 4
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assert root.left.data == 2
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assert root.left.left.data == 1
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assert root.left.left.left == nil
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assert root.left.left.right == nil
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assert root.left.right.data == 3
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assert root.left.right.left == nil
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assert root.left.right.right == nil
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assert root.right.data == 6
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assert root.right.left.data == 5
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assert root.right.left.left == nil
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assert root.right.left.right == nil
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assert root.right.right.data == 7
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assert root.right.right.left == nil
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assert root.right.right.right == nil
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end
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describe "can sort data" do
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test "can sort single number" do
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root = BinarySearchTree.new(2)
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assert [2] == BinarySearchTree.in_order(root)
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end
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test "can sort if second number is smaller than first" do
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root =
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BinarySearchTree.new(2)
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|> BinarySearchTree.insert(1)
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assert [1, 2] == BinarySearchTree.in_order(root)
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end
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test "can sort if second number is the same as the first" do
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root =
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BinarySearchTree.new(2)
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|> BinarySearchTree.insert(2)
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assert [2, 2] == BinarySearchTree.in_order(root)
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end
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test "can sort if second number is greater than the first" do
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root =
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BinarySearchTree.new(2)
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|> BinarySearchTree.insert(3)
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assert [2, 3] == BinarySearchTree.in_order(root)
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end
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test "can sort complex tree" do
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root =
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BinarySearchTree.new(2)
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|> BinarySearchTree.insert(1)
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|> BinarySearchTree.insert(3)
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|> BinarySearchTree.insert(6)
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|> BinarySearchTree.insert(7)
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|> BinarySearchTree.insert(5)
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assert [1, 2, 3, 5, 6, 7] == BinarySearchTree.in_order(root)
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end
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end
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end
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ExUnit.start()
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ExUnit.configure(exclude: :pending, trace: true)
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