I have actually implemented memoized graph traversals for work (unlike most programmers). To begin with, I see no point in asking this when I could ask how to implement trait checking in Rust (what I had to use memoized graph traversals for), which a practitioner will find much more intuitive.

Moreover, memoized graph traversals don't get you full credit on this question. There's a dynamic programming solution, and in fact the ideal solution is one using matrix math, which is ludicrously divorced from anything most programmers would ever see.