Andres
Hello.
Trying to find the only element that does not appear twice I wrote the following algorithm:
list = [1, 2, 3, 1, 3, 10, 200, 10, 200] # Expected result => 2
def single_one(list) do
list
|> Enum.reduce(%MapSet{}, fn x, acc ->
if MapSet.member?(acc, x) do
MapSet.delete(acc, x)
else
MapSet.put(acc, x)
end
end)
|> MapSet.to_list()
|> hd()
end
I have the following questions:
- I would like to know if in Elixir it is good practice to use if else as I did in the previous algorithm.
I could not find a way to access the first and only element of the MapSet.
I proceeded to convert the MapSet into a list and then its head. - Is there a better way to get the first element of a MapSet?
Any suggestions to improve the algorithm is welcome.
Thanks.
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Qqwy
In cases like this, where you check for a boolean result,
.
if/elseis usually used instead ofcase, so it’s good as isI don’t think there is, because there is no ‘first’ element in a MapSet. In this case, you know that there is only a single one, but in the more general case, elements inside a MapSet are not ordered. So if you have more than a single element in a set, there is no idea which element you’d obtain when extracting a single one from it.
Andres
Hi @Qqwy. Thanks for your response.
Could you be so kind to explain me how I can refer to the first element of a MapSet? Or what do you mean there is not a first element in a MapSet?
The official definition of MapSet says the following:
Thanks so much!
tty
I would suggest something similar to a counting sort. That would only take O(2n) if you know the range O(3n) if you don’t.
peerreynders
Elements in Maps and MapSets are not ordered. So whichever element appears “first” is “random”, i.e. is implementation dependent.
mudasobwa
hauleth
Classic methods are always the best one.
Andres
Hi @peerreynders.
Thank you very much for clarifying my question.
Andres
Hello @mudasobwa
This is amazing:
Thanks so much for sharing!
NobbZ
This will fail badly when someone puts a number thrice…
peerreynders
Find the element that appears once in an array where every other element appears twice
Feels like a solution that was looking for a problem statement