Define Math module
Support `Math.factor` and cover it with tests.
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26
assessments/semiprimes/server/lib/math.ex
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26
assessments/semiprimes/server/lib/math.ex
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defmodule Math do
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@moduledoc """
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Math utilities.
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"""
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alias Extras
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@doc """
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Returns the prime factors for `n`.
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## Examples
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iex> Math.factor(15)
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[3, 5]
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"""
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def factor(1), do: []
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def factor(n) do
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Extras.range(2, n - 1)
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|> Enum.find(&(rem(n, &1) == 0))
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|> case do
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nil -> [n]
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x -> [x | factor(div(n, x))]
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end
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end
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end
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32
assessments/semiprimes/server/test/math_test.exs
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32
assessments/semiprimes/server/test/math_test.exs
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defmodule MathTest do
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use ExUnit.Case
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doctest Math
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describe "factor" do
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test "returns the prime factors for an input" do
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[
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{15, [3, 5]},
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{12, [2, 2, 3]},
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{9, [3, 3]},
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{21, [3, 7]}
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]
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|> Enum.map(fn {input, expected} ->
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Math.factor(input) == expected
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end)
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|> Enum.all?()
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|> assert
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end
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test "handles large numbers" do
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assert Math.factor(104_023) == [17, 29, 211]
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end
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test "returns an empty list for 1" do
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assert Math.factor(1) == []
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end
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test "returns the prime number itself when the input is prime" do
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assert Math.factor(7) == [7]
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end
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end
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end
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