defmodule Solution do

@spec three_sum(nums :: [integer]) :: [[integer]]

def three_sum(nums) do

length_of_nums = length nums

num_index_map = nums |> Enum.with_index |> Map.new

frequencies_of_num = nums |> Enum.frequencies()

tuple_nums = nums |> List.to_tuple

num_indexs_map = nums |>

Enum.with_index() |>

Enum.group_by(fn {v, _} -> v end, fn {_, i} -> i end)

Stream.unfold({0, 1}, fn {i, j} ->

if j < length_of_nums - 1,

do: {{i, j}, {i, j + 1}},

else: {{i, j}, {i + 1, i + 2}}

end) |>

Stream.take_while(fn {i, _} ->

i < length_of_nums - 1

end) |>

Stream.map(fn {i, j} ->

a = elem tuple_nums, i

b = elem tuple_nums, j

c = -(a + b)

case frequencies_of_num[c] do

nil -> nil

count when count >= 3 -> [a, b, c] |> Enum.sort()

_ ->

if num_indexs_map[c] |> Enum.filter(& &1 != i && &1 != j) |> Enum.at(0),

do: [a, b, c] |> Enum.sort(),

else: nil

end

end) |>

Stream.reject(& &1 == nil) |>

Stream.uniq |>

Enum.to_list

end

end