Longest Substring Without Repeating Characters

Problem

Return the length of the longest substring with all unique characters.

Example 1

Input: s = "abcabcbb"
Output: 3

Constraints

• 0 <= s.length <= 5 * 10^4

Notes

• Focus on the underlying sliding window pattern.
• Write the cleanest correct solution before optimizing further.
• Hidden tests cover larger edge cases than the visible examples.