Longest Substring Without Repeating Characters

Also reported as LeetCode 3

CodingMicrosoftLast reported January 2026Low Frequency

Reported: 2× across candidate reports
First seen: December 2025
Last reported: January 2026
Reported outcome: unknown

Problem Overview

Microsoft coding question, reconstructed from 2 candidate reports (December 2025 to January 2026). The write-up includes a Python solution that passes 5 test cases.

The full problem statement — full requirements, constraints, and edge cases
Approach and trade-offs — what passing candidates did, and the mistakes that sink people

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Verified Source

Every question is reconstructed from multiple independent candidate reports. Follow-ups candidates reported, not invented ones.

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Interviewer Follow-ups

The follow-ups candidates reported, with the trigger that prompts each one — plus the mistakes that sink people.