Although tree traversal is a powerful algorithm, this representation seems to offer an alternative implementation. If we know the index of the last non-null value (approx. lastItem = root.length), would something like Math.log(last item) / Math.log(2) be correct? +-1?

How interesting. What a striking story. It reminds me of my path. When I started college, I had no information about a career in software. I wound up in Physics rather than Electronics, but with similar results. My classwork cratered in my third year. The odd part is that my story starts in the 1970’s. Even though I was attending high school in Silicon Valley (San Jose), the idea of writing software professionally never came up. I switched to Computer Science, and it’s all been uphill since. After graduating in the early 1980’s, I’ve worked at Boeing, Microsoft, Google, and a few others. It’s been a delight keeping up with the evolving technology. I later completed a Master’s degree in Computer Science. Almost the entire time has been building distributed software systems of ever increasing scale.

No surprise, the memorization of training data is confirmed in the LLM literature. https://iclr.cc/virtual/2023/oral/12637