pascals_triangle
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{
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"authors": [
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"dalexj"
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],
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"contributors": [
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"amencarini",
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"angelikatyborska",
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"Cohen-Carlisle",
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"devonestes",
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"lpil",
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"neenjaw",
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"parkerl",
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"sotojuan",
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"waiting-for-dev"
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],
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"files": {
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"solution": [
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"lib/pascals_triangle.ex"
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],
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"test": [
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"test/pascals_triangle_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": "Compute Pascal's triangle up to a given number of rows.",
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"source": "Pascal's Triangle at Wolfram Math World",
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"source_url": "https://www.wolframalpha.com/input/?i=Pascal%27s+triangle"
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}
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{"track":"elixir","exercise":"pascals-triangle","id":"71d888253d44412db03d365e545aa233","url":"https://exercism.org/tracks/elixir/exercises/pascals-triangle","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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pascals_triangle-*.tar
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@ -0,0 +1,75 @@
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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/pascals_triangle.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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# Pascal's Triangle
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Welcome to Pascal's Triangle 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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Compute Pascal's triangle up to a given number of rows.
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In Pascal's Triangle each number is computed by adding the numbers to the right and left of the current position in the previous row.
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```text
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1
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1 1
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1 2 1
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1 3 3 1
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1 4 6 4 1
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# ... etc
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```
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## Source
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### Created by
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- @dalexj
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### Contributed to by
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- @amencarini
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- @angelikatyborska
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- @Cohen-Carlisle
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- @devonestes
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- @lpil
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- @neenjaw
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- @parkerl
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- @sotojuan
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- @waiting-for-dev
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### Based on
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Pascal's Triangle at Wolfram Math World - https://www.wolframalpha.com/input/?i=Pascal%27s+triangle
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defmodule PascalsTriangle do
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@doc """
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Calculates the rows of a pascal triangle
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with the given height
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"""
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@spec rows(integer) :: [[integer]]
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def rows(num) do
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1..num
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|> Enum.reduce([[]], fn _, triangle -> [next(hd(triangle)) | triangle] end)
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|> Enum.take(num)
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|> Enum.reverse
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end
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defp next(from, acc \\ [])
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defp next([], _acc), do: [1]
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defp next([1], _acc), do: [1, 1]
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defp next([one, two | []], acc), do: [1 | Enum.reverse([1, one + two | acc])]
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defp next([one, two | rest], acc), do: next([two | rest], [one + two | acc])
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end
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defmodule PascalsTriangle.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: :pascals_triangle,
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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 PascalsTriangleTest do
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use ExUnit.Case
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test "one row" do
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assert PascalsTriangle.rows(1) == [[1]]
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end
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test "two rows" do
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assert PascalsTriangle.rows(2) == [[1], [1, 1]]
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end
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test "three rows" do
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assert PascalsTriangle.rows(3) == [[1], [1, 1], [1, 2, 1]]
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end
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test "four rows" do
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assert PascalsTriangle.rows(4) == [[1], [1, 1], [1, 2, 1], [1, 3, 3, 1]]
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end
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test "five rows" do
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assert PascalsTriangle.rows(5) == [[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1]]
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end
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test "six rows" do
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assert PascalsTriangle.rows(6) == [
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[1],
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[1, 1],
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[1, 2, 1],
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[1, 3, 3, 1],
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[1, 4, 6, 4, 1],
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[1, 5, 10, 10, 5, 1]
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]
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end
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test "ten rows" do
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assert PascalsTriangle.rows(10) == [
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[1],
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[1, 1],
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[1, 2, 1],
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[1, 3, 3, 1],
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[1, 4, 6, 4, 1],
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[1, 5, 10, 10, 5, 1],
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[1, 6, 15, 20, 15, 6, 1],
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[1, 7, 21, 35, 35, 21, 7, 1],
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[1, 8, 28, 56, 70, 56, 28, 8, 1],
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[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]
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]
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end
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test "20 rows" do
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assert PascalsTriangle.rows(20) == [
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[1],
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[1, 1],
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[1, 2, 1],
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[1, 3, 3, 1],
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[1, 4, 6, 4, 1],
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[1, 5, 10, 10, 5, 1],
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[1, 6, 15, 20, 15, 6, 1],
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[1, 7, 21, 35, 35, 21, 7, 1],
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[1, 8, 28, 56, 70, 56, 28, 8, 1],
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[1, 9, 36, 84, 126, 126, 84, 36, 9, 1],
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[1, 10, 45, 120, 210, 252, 210, 120, 45, 10, 1],
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[1, 11, 55, 165, 330, 462, 462, 330, 165, 55, 11, 1],
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[1, 12, 66, 220, 495, 792, 924, 792, 495, 220, 66, 12, 1],
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[1, 13, 78, 286, 715, 1287, 1716, 1716, 1287, 715, 286, 78, 13, 1],
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[1, 14, 91, 364, 1001, 2002, 3003, 3432, 3003, 2002, 1001, 364, 91, 14, 1],
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[1, 15, 105, 455, 1365, 3003, 5005, 6435, 6435, 5005, 3003, 1365, 455, 105, 15, 1],
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[
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1,
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16,
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120,
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560,
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1820,
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4368,
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8008,
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11440,
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12870,
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11440,
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8008,
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4368,
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1820,
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560,
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120,
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16,
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1
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],
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[
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1,
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17,
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136,
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680,
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2380,
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6188,
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12376,
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19448,
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24310,
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24310,
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19448,
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12376,
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6188,
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2380,
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680,
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136,
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17,
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1
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],
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[
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1,
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18,
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153,
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816,
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3060,
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8568,
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18564,
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31824,
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43758,
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48620,
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43758,
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31824,
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18564,
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8568,
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3060,
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816,
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153,
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18,
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1
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],
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[
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1,
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19,
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171,
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969,
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3876,
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11628,
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27132,
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50388,
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75582,
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92378,
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92378,
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75582,
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50388,
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27132,
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11628,
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3876,
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969,
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171,
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19,
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1
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]
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]
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end
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end
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@ -0,0 +1,2 @@
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ExUnit.start()
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ExUnit.configure(exclude: :pending, trace: true)
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