Longest Single-Letter Substring After at Most k Letter Replacements

Company: Microsoft

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Onsite

Overview: A string problem: given uppercase letters and a budget of k single-letter changes, find the longest contiguous substring that can be turned into one repeated letter. It tests efficient substring scanning with letter counts and careful reasoning about when a candidate substring stays valid.

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