Define Math module

Support `Math.factor` and cover it with tests.
This commit is contained in:
William Carroll 2020-12-11 22:43:26 +00:00
parent 6af5e4b82e
commit f1e4582392
2 changed files with 58 additions and 0 deletions

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defmodule Math do
@moduledoc """
Math utilities.
"""
alias Extras
@doc """
Returns the prime factors for `n`.
## Examples
iex> Math.factor(15)
[3, 5]
"""
def factor(1), do: []
def factor(n) do
Extras.range(2, n - 1)
|> Enum.find(&(rem(n, &1) == 0))
|> case do
nil -> [n]
x -> [x | factor(div(n, x))]
end
end
end

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defmodule MathTest do
use ExUnit.Case
doctest Math
describe "factor" do
test "returns the prime factors for an input" do
[
{15, [3, 5]},
{12, [2, 2, 3]},
{9, [3, 3]},
{21, [3, 7]}
]
|> Enum.map(fn {input, expected} ->
Math.factor(input) == expected
end)
|> Enum.all?()
|> assert
end
test "handles large numbers" do
assert Math.factor(104_023) == [17, 29, 211]
end
test "returns an empty list for 1" do
assert Math.factor(1) == []
end
test "returns the prime number itself when the input is prime" do
assert Math.factor(7) == [7]
end
end
end