A-Star Algorithm
A neat algorithm for finding a short path through a graph is A-Star. It's used in a lot of games for the characters to find paths through a map.
One thing that's fun about this algorithm is that it's traditionally formulated in terms of mutable data structures. What would this look like as a functional implementation?
Your task is to implement A-Star in Clojure. You can use mutable state if you want! The Wikipedia page has a good description of the algorithm.