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merge.ex
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merge.ex
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defmodule ExAlgo.Sort.Merge do
@moduledoc """
Implements sorting algorithms based on exchanges.
"""
@type item :: any()
@type t :: [item()]
@doc """
Perform sort by using the merge_sort algorithm.
## Example
iex> Merge.merge_sort([])
[]
iex> Merge.merge_sort([1])
[1]
iex> Merge.merge_sort([3, 2, 1])
[1, 2, 3]
iex> Merge.merge_sort([2, 7, -1, 5])
[-1, 2, 5, 7]
"""
@spec merge_sort(t) :: t
def merge_sort([]), do: []
def merge_sort([_] = list), do: list
def merge_sort(list) do
half = list |> length() |> div(2)
list
|> Enum.split(half)
|> then(fn {left, right} ->
{merge_sort(left), merge_sort(right)}
end)
|> then(fn {left, right} -> merge(left, right) end)
end
@spec merge(t, t) :: t
defp merge([], right), do: right
defp merge(left, []), do: left
defp merge([x | xs], [y | _] = right) when x < y, do: [x | merge(xs, right)]
defp merge(left, [y | ys]), do: [y | merge(ys, left)]
end