Leetcode 3. Longest Substring Without Repeating Characters
Find the length of the longest contiguous substring that contains no repeated characters. This is a classic sliding-window / two-pointer problem where you track seen characters to expand and contract the window efficiently (linear-time expected).
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Early January, 2026
Zscaler
Staff
Mid December, 2025
Expedia
Mid-level
modified version of *LeetCode 3 Given a string s, find the length of the longest substring that contains no repeated **letters**, treating uppercase and lowercase versions of the same letter as identical. All characters are allowed in the substring, including digits, symbols, and punctuation. However, only alphabetic characters (A–Z, a–z) participate in the “no-repeat” restriction. Non-alphabet characters do not affect uniqueness rules, but they still count toward the substring length.
Early October, 2025
Amazon
Mid-level
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