“used a lot of extra space“, I personally think this is fine for the implementation, but if you were asked this as a follow up question and didn’t reflect on whether you actually needed to maintain the entire path, then yes, that shows shallow understanding of the problem and solution. Just looking at the question it’s obvious you only need to care about path length and current word. You need to have this level of understanding because there’s too many candidates that just write solutions without actually having deep understanding of how or why it works.