Given n integers and a value K, we want to find the indices of the pair of numbers such that the pair adds up to the given value K and return −1, −1 if no such pair exists.
Addends.find takes a list as its first argument and an integer, k, as its second argument. It returns a list of tuples like [{0, 15}, {1, 14}] if it was able to find a pair of integers that sums up to k or else it returns -1. The numbers in the tuples are the index of desired integers in the original list. Addends.find also checks to see if all the elements of the given list are appropriate otherwise it raises an error. For considered edge cases please take a look at addends_finder_test.exs.
A few example
iex(2)> Addends.find([1, 2, 3, 9], 8)
-1iex(3)> Addends.find([1, 2, 4, 4], 8)
[{2, 3}]iex(4)> Addends.find([4, 2, 1, 4], 8)
[{0, 3}]# This takes around 4s in my 7 years old laptop (including the creation of list)
iex(5)> list = 0..10_000_000 |> Enum.into([])
iex(6)> Addends.find(list, 15)
[{0, 15}, {1, 14}, {2, 13}, {3, 12}, {4, 11}, {5, 10}, {6, 9}, {7, 8}]iex(10)> Addends.find([4, -12, 1, 4], 8)
** (ArgumentError) Nah! the given list should not have any negative integer
addends_finder.exs:31: Addends.do_filter/2
(elixir) lib/enum.ex:814: anonymous fn/3 in Enum.filter/2
(elixir) lib/enum.ex:1755: Enum."-reduce/3-lists^foldl/2-0-"/3
(elixir) lib/enum.ex:814: Enum.filter/2
addends_finder.exs:13: Addends.find/2