Implement a Removable Nested-List Iterator
Company: Airbnb
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
Overview: Implement an iterator over mutable nested integer lists with repeatable lookahead and a legal once-per-item removal operation. Preserve traversal order through empty rows and deletions, expose mutations in the original input, and define exhaustion and illegal-state behavior precisely.