About this challenge
Longest Substring Without Repeats is a medium string manipulation coding challenge. It tests string-manipulation techniques: parsing, transforming, and searching text efficiently. Write your solution in the editor above, run it against the test cases, and get instant feedback — free, in your browser, no sign-up.
Show a hint & approach (spoiler)
Hint: Sliding window with a Set. When you hit a duplicate, shrink from the left until the duplicate is gone.
Keep practicing
Browse all coding challenges, or build intuition for the underlying concepts with the algorithm visualizers and the developer cheatsheets.