def is_unique_chars_v3(str):
    """
    If not allowed to use additional data structures, we can compare every character of the string to every other
    character of the string.
    This will take 0(n ** 2) time and 0(1) space
    """
    for char1 in str:
        occurrence = 0
        for char2 in str:
            if char1 == char2:
                occurrence += 1
            if occurrence > 1:
                return False
    return True