RESTRICTIONS: - Do not add any imports and do it on python .Do not use recursion. Do not use break/continue.Do not use try-except statements. def longest_unique_substring(s: str) -> str: """ Given a...

RESTRICTIONS:

   - Do not add any imports and do it on python .Do not use recursion. Do not use break/continue.Do not use try-except statements.

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).


For this question, PERFORMANCE WILL MATTER, and we will run long tests with
up to 10,000,000 characters as an input. To get full credit, an input of
10,000,000 characters should return the correct answer within 60 seconds
(the instructor solution takes about 2).


Helpful tips:
In order to get your function to run fast, consider using a dictionary to
store the indexes of previously seen characters, from there, you can
follow a set of rules based on each new character you see to determine
the length of the longest unique substring seen so far.