Return true if a list has duplicates otherwise false

def has_duplicates?(list) do
  list
  |> Enum.reduce_while([], fn x, acc ->
    if x in acc, do: {:halt, 0}, else: {:cont, [x | acc]}
  end)
  |> is_integer()
end

Welcome,

Maybe You can compare the length of original list with the one You get from Enum.uniq

Maybe something like this:

def has_duplicates?(list), do: Enum.uniq(list) != list

@l00ker in your case list will be iterated twice - first to make uniq and second to compare with original list

Hi @l00ker
Very nice one liner!
Thanks so much!

Thanks so much @alexiss.
I really liked:

if x in acc, do: {:halt, 0}, else: {:cont, [x | acc]}

and

|> is_integer()

I changed my code like this:

def has_duplicates?(list) do
    list
    |> Enum.reduce_while([], fn x, acc ->
      if x in acc, do: {:halt, false}, else: {:cont, [x | acc]}
    end)
    |> is_boolean()
  end

Thanks so much for your help and ideas!

But reducing and finding the elements in a list again results in a runtime of O(n log n), using a MapSet is O(n).

Agree, I miss it. The final proposal whould be:

def has_duplicates?(list) do
  list
  |> Enum.reduce_while(%MapSet{}, fn x, acc ->
    if MapSet.member?(acc, x), do: {:halt, false}, else: {:cont, MapSet.put(acc, x)}
  end)
  |> is_boolean()
end

Hi @NobbZ
Thanks so much for your help.

Beautiful @alexiss

def has_duplicates?(list) do
  list
  |> Enum.reduce_while(%MapSet{}, fn x, acc ->
    if MapSet.member?(acc, x), do: {:halt, false}, else: {:cont, MapSet.put(acc, x)}
  end)
  |> is_boolean()
end

I learned so much!
Thanks so much @NobbZ and @alexiss!