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# Lucassifoni's solution

## to Allergies in the Elixir Track

Published at May 27 2019 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.

An allergy test produces a single numeric score which contains the information about all the allergies the person has (that they were tested for).

The list of items (and their value) that were tested are:

• eggs (1)
• peanuts (2)
• shellfish (4)
• strawberries (8)
• tomatoes (16)
• chocolate (32)
• pollen (64)
• cats (128)

So if Tom is allergic to peanuts and chocolate, he gets a score of 34.

Now, given just that score of 34, your program should be able to say:

• Whether Tom is allergic to any one of those allergens listed above.
• All the allergens Tom is allergic to.

Note: a given score may include allergens not listed above (i.e. allergens that score 256, 512, 1024, etc.). Your program should ignore those components of the score. For example, if the allergy score is 257, your program should only report the eggs (1) allergy.

## Running tests

Execute the tests with:

``````\$ elixir allergies_test.exs
``````

### Pending tests

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
``````

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

## Source

Jumpstart Lab Warm-up http://jumpstartlab.com

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### allergies_test.exs

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
Code.load_file("allergies.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule AllergiesTest do
use ExUnit.Case

# @tag :pending
test "no_allergies_at_all" do
Allergies.list(0) |> assert_is_a_set_containing([])
end

@tag :pending
test "allergic_to_just_eggs" do
Allergies.list(1) |> assert_is_a_set_containing(~w[eggs])
end

@tag :pending
test "allergic_to_just_peanuts" do
Allergies.list(2) |> assert_is_a_set_containing(~w[peanuts])
end

@tag :pending
test "allergic_to_just_strawberries" do
Allergies.list(8) |> assert_is_a_set_containing(~w[strawberries])
end

@tag :pending
test "allergic_to_eggs_and_peanuts" do
Allergies.list(3) |> assert_is_a_set_containing(~w[eggs peanuts])
end

@tag :pending
test "allergic_to_more_than_eggs_but_not_peanuts" do
Allergies.list(5) |> assert_is_a_set_containing(~w[eggs shellfish])
end

@tag :pending
test "allergic_to_lots_of_stuff" do
Allergies.list(248)
|> assert_is_a_set_containing(~w[strawberries tomatoes chocolate pollen cats])
end

@tag :pending
test "allergic_to_everything" do
Allergies.list(255)
|> assert_is_a_set_containing(
~w[eggs peanuts shellfish strawberries tomatoes chocolate pollen cats]
)
end

@tag :pending
test "no_allergies_means_not_allergic" do
refute Allergies.allergic_to?(0, "peanuts")
refute Allergies.allergic_to?(0, "cats")
refute Allergies.allergic_to?(0, "strawberries")
end

@tag :pending
test "is_allergic_to_eggs" do
assert Allergies.allergic_to?(1, "eggs")
end

@tag :pending
test "allergic_to_eggs_in_addition_to_other_stuff" do
assert Allergies.allergic_to?(5, "eggs")
end

@tag :pending
test "ignore_non_allergen_score_parts" do
Allergies.list(509)
|> assert_is_a_set_containing(~w[eggs shellfish strawberries tomatoes chocolate pollen cats])
end

defp assert_is_a_set_containing(list, to_contain) do
set = Enum.into(list, MapSet.new())

same_contents =
to_contain
|> Enum.into(MapSet.new())
|> MapSet.equal?(set)

assert same_contents,
"Expected a set with: #{inspect(to_contain)} got #{inspect(set |> MapSet.to_list())}"
end
end``````
``````defmodule Allergies do
use Bitwise

def list(flags), do: flags |> map_flags

def map_flags(flags) do
[
"eggs",
"peanuts",
"shellfish",
"strawberries",
"tomatoes",
"chocolate",
"pollen",
"cats"
] |> Enum.with_index
|> Enum.reduce(MapSet.new(), fn {a, i}, set -> flag_if(set, flags, a, (:math.pow(2, i)|> round)) end)
end

def flag_if(xs, input, x, mask), do: if (input &&& mask) === mask, do: MapSet.put(xs, x), else: xs
def allergic_to?(flags, item), do: MapSet.subset?(Enum.into([item], MapSet.new()), list(flags))
end``````

### What can you learn from this solution?

A huge amount can be learned from reading other peopleâ€™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.

• What compromises have been made?
• Are there new concepts here that you could read more about to improve your understanding?