def two_number_sum(array, target_sum):
    """
        two_number_sum finds the two numbers whose sum is equals to target_sum

        array: the collection of numbers that can sum the target_sum.
        target_sum: the target number to find

        returns a list with the two numbars that sums the target number.
        if there are not number that can sum the target, it returns an empty list.

    """
    hash_table = {}

    i = 0
    while i < len(array):
        result = target_sum - array[i]

        if result in hash_table:
            return [result, array[i]]
        else:
            current = array[i]
            hash_table[current] = i

        i = i + 1

    return []