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Find longest unique substring

Lowe'sSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenCoding & Algorithms

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This interview question evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer for Find longest unique substring states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Given a string s, find the length and one example of the longest substring of s that contains no repeated characters. If multiple answers exist, return any valid one. Explain your algorithm, prove its correctness at a high level, analyze time and space complexity, and discuss edge cases (e.g., empty string, all identical characters, presence of Unicode code points).