Editor

Longest Substring Without Repeats

Advanced · Write the code · from 50 Python Practice Problems with Instant Answer Checking (Beginner to Advanced)

From the lesson: 50 Python Practice Problems with Instant Answer Checking (Beginner to Advanced)

Fifty problems, each with a code editor and real tests. Write your solution, press Check, and see exactly which cases pass. Stuck? Hints reveal one at a time, and the solution unlocks once you have checked at least once. Your code and progress are saved in this browser.

Read the lesson

Write longest_unique(s) that returns the length of the longest substring with no repeated characters.

longest_unique("abcabcbb")  ->  3   ("abc")
longest_unique("pwwkew")    ->  3   ("wke")
def longest_unique(s):
pass
Solution unlocks after your first Check

What Check runs

Your code runs first, then each of these lines. The output must match exactly.

RunsExpected output
longest_unique("abcabcbb")3
longest_unique("pwwkew")3

More practice problems

All Python exercises · 50 practice problems