algorithm A graph search algorithm. A* is guaranteed to

find a minimal solution path before any other solution paths,

if a solution exists, in other words, it is an "admissible"

search algorithm. Each path is assigned a value based on the

cost of the path (e.g. its length) and an (under)estimate of

the cost of completing the path, i.e. the cost of a path from

the end of the current path to a solution.