Memoization trades compute time for memory: you reduce CPU cost by 90% _at the cost_ of some memory. The author measured one, but it doesn't look like they measured the other.
It's an important detail to take into account. I'm sure this optimization makes sense, and the size of additional memory is not that big, but I believe it's good to "measure, not assume" as some load bearing model might say.
It's an important detail to take into account. I'm sure this optimization makes sense, and the size of additional memory is not that big, but I believe it's good to "measure, not assume" as some load bearing model might say.