"""
    Difficulty: ***
    Code: ****

    Given an array of numbers arr and a number S, find 4 different numbers in arr that sum up to S.

    Write a function that gets arr and S and returns an array with 4 indices of such numbers in arr,
     or null if no such combination exists.
    Explain and code the most efficient solution possible, and analyze its runtime and space complexity.

    Ref: http://stackoverflow.com/questions/2459653/how-to-find-smallest-substring-which-contains-all-characters-from-a-given-string


"""
import unittest



class MyTestCases(unittest.TestCase):
    def test_quad_combinations(self):
        pass
