Take a nested list and return a single flattened list with all values except nil/null.
The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.
For Example
input: [1,[2,3,null,4],[null],5]
output: [1,2,3,4,5]
Execute the tests with:
$ elixir flatten_array_test.exs
In the test suites, all but the first test have been skipped.
Once you get a test passing, you can unskip the next one by
commenting out the relevant @tag :pending
with a #
symbol.
For example:
# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
Or, you can enable all the tests by commenting out the
ExUnit.configure
line in the test suite.
# ExUnit.configure exclude: :pending, trace: true
For more detailed information about the Elixir track, please see the help page.
Interview Question https://reference.wolfram.com/language/ref/Flatten.html
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
if !System.get_env("EXERCISM_TEST_EXAMPLES") do
Code.load_file("flatten_array.exs", __DIR__)
end
ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule FlattenArrayTest do
use ExUnit.Case
test "returns original list if there is nothing to flatten" do
assert FlattenArray.flatten([1, 2, 3]) == [1, 2, 3]
end
@tag :pending
test "flattens an empty nested list" do
assert FlattenArray.flatten([[]]) == []
end
@tag :pending
test "flattens a nested list" do
assert FlattenArray.flatten([1, [2, [3], 4], 5, [6, [7, 8]]]) == [1, 2, 3, 4, 5, 6, 7, 8]
end
@tag :pending
test "removes nil from list" do
assert FlattenArray.flatten([1, nil, 2]) == [1, 2]
end
@tag :pending
test "removes nil from a nested list" do
assert FlattenArray.flatten([1, [2, nil, 4], 5]) == [1, 2, 4, 5]
end
@tag :pending
test "returns an empty list if all values in nested list are nil" do
assert FlattenArray.flatten([nil, [nil], [nil, [nil]]]) == []
end
end
defmodule Flattener do
# still got to be a better way X_X
@doc """
Accept a list and return the list flattened without nil values.
## Examples
iex> Flattener.flatten([1, [2], 3, nil])
[1,2,3]
iex> Flattener.flatten([nil, nil])
[]
"""
@spec flatten(list) :: list
def flatten([]), do: []
def flatten([[]|t]), do: flatten(t)
def flatten([nil|t]), do: flatten(t)
def flatten([h|t]) when is_list(h), do: flatten(h) ++ flatten(t)
def flatten([h|t]), do: [h|flatten(t)]
end
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.
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