Given two lists determine if the first list is contained within the second list, if the second list is contained within the first list, if both lists are contained within each other or if none of these are true.
Specifically, a list A is a sublist of list B if by dropping 0 or more elements from the front of B and 0 or more elements from the back of B you get a list that's completely equal to A.
Examples:
Execute the tests with:
$ elixir sublist_test.exs
In the test suites, all but the first test have been skipped.
Once you get a test passing, you can unskip the next one by
commenting out the relevant @tag :pending
with a #
symbol.
For example:
# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
Or, you can enable all the tests by commenting out the
ExUnit.configure
line in the test suite.
# ExUnit.configure exclude: :pending, trace: true
For more detailed information about the Elixir track, please see the help page.
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
if !System.get_env("EXERCISM_TEST_EXAMPLES") do
Code.load_file("sublist.exs", __DIR__)
end
ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule SublistTest do
use ExUnit.Case
test "empty equals empty" do
assert Sublist.compare([], []) == :equal
end
@tag :pending
test "empty is a sublist of anything" do
assert Sublist.compare([], [nil]) == :sublist
end
@tag :pending
test "anything is a superlist of empty" do
assert Sublist.compare([nil], []) == :superlist
end
@tag :pending
test "1 is not 2" do
assert Sublist.compare([1], [2]) == :unequal
end
@tag :pending
test "comparing massive equal lists" do
l = Enum.to_list(1..1_000_000)
assert Sublist.compare(l, l) == :equal
end
@tag :pending
test "sublist at start" do
assert Sublist.compare([1, 2, 3], [1, 2, 3, 4, 5]) == :sublist
end
@tag :pending
test "sublist in middle" do
assert Sublist.compare([4, 3, 2], [5, 4, 3, 2, 1]) == :sublist
end
@tag :pending
test "sublist at end" do
assert Sublist.compare([3, 4, 5], [1, 2, 3, 4, 5]) == :sublist
end
@tag :pending
test "partially matching sublist at start" do
assert Sublist.compare([1, 1, 2], [1, 1, 1, 2]) == :sublist
end
@tag :pending
test "sublist early in huge list" do
assert Sublist.compare([3, 4, 5], Enum.to_list(1..1_000_000)) == :sublist
end
@tag :pending
test "huge sublist not in huge list" do
assert Sublist.compare(Enum.to_list(10..1_000_001), Enum.to_list(1..1_000_000)) == :unequal
end
@tag :pending
test "superlist at start" do
assert Sublist.compare([1, 2, 3, 4, 5], [1, 2, 3]) == :superlist
end
@tag :pending
test "superlist in middle" do
assert Sublist.compare([5, 4, 3, 2, 1], [4, 3, 2]) == :superlist
end
@tag :pending
test "superlist at end" do
assert Sublist.compare([1, 2, 3, 4, 5], [3, 4, 5]) == :superlist
end
@tag :pending
test "1 and 2 does not contain 3" do
assert Sublist.compare([1, 2], [3]) == :unequal
end
@tag :pending
test "partially matching superlist at start" do
assert Sublist.compare([1, 1, 1, 2], [1, 1, 2]) == :superlist
end
@tag :pending
test "superlist early in huge list" do
assert Sublist.compare(Enum.to_list(1..1_000_000), [3, 4, 5]) == :superlist
end
@tag :pending
test "strict equality needed" do
assert Sublist.compare([1], [1.0, 2]) == :unequal
end
@tag :pending
test "recurring values sublist" do
assert Sublist.compare([1, 2, 1, 2, 3], [1, 2, 3, 1, 2, 1, 2, 3, 2, 1]) == :sublist
end
@tag :pending
test "recurring values unequal" do
assert Sublist.compare([1, 2, 1, 2, 3], [1, 2, 3, 1, 2, 3, 2, 3, 2, 1]) == :unequal
end
end
defmodule Sublist do
@doc """
Returns whether the first list is a sublist or a superlist of the second list
and if not whether it is equal or unequal to the second list.
"""
def compare(list1, list2) do
cond do
equal?(list1, list2) -> :equal
sublist?(list1, list2) -> :sublist
superlist?(list1, list2) -> :superlist
true -> :unequal
end
end
defp equal?(list, list), do: true
defp equal?(list1, list2), do: false
defp sublist?([], _), do: true
defp sublist?([h | t], []), do: false
defp sublist?(list1, list2) do
starts_with?(list1, list2) || sublist?(list1, tl(list2))
end
defp superlist?(list1, list2), do: sublist?(list2, list1)
defp starts_with?([], _), do: true
defp starts_with?([h | t1], [h | t2]), do: starts_with?(t1, t2)
defp starts_with?(list1, list2), do: false
end
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