LAB RESTRICTIONS, PLEASE READ: - Do not add any imports, the ones that you need will be given to you. - Do not use recursion. - Do not use try-except statements, you should be able to anticipate or...

LAB RESTRICTIONS, PLEASE READ:
- Do not add any imports, the ones that you need will be given to you.
- Do not use recursion.
- Do not use try-except statements, you should be able to anticipate
or prevent any errors from happening at all!

- Code in python

- Should work for given doctest

def longest_unique_substring(s: str) -> str:
"""
Given a string
, return the longest unique substring that occurs within

.


A unique substring is a substring within

which DOES NOT have any
repeating characters. As an example, "xd" is unique but "xxd" is not.


If there are two equal length unique substrings within
, return the one
that starts first (i.e., begins at a smaller index).