Given the root of a binary tree, return the vertical order traversal of its node values from top to bottom, column by column. Nodes in the same row and column should be ordered left to right.

"The process was first a phone screen followed by a virtual loop with four rounds. The phone screen was a single tree traversal coding problem, and the onsite had two coding rounds, one system design round, and one behavioral round. The most interesting part was a new AI coding section that I hadn't seen before. It sounded new enough that even the format felt a little flexible, but the expectation was still that I do the actual coding myself and only use AI in a limited way. Overall it was pretty challenging, and if I did it again I would spend more time on behavioral prep because that was my weakest part."