Brute force: check every substring, verify no duplicates. That's . The sliding window idea: maintain a window [left, right] of unique characters. Expand right to grow the window. When you hit a duplicate, shrink from left until the duplicate is removed. Use a set to track which characters are in the current window.
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$ curl repovive.com/roadmaps/maang-interview-prep/two-pointers-sliding-window/longest-substring-without-repeating-hint
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