algorithm starts at the root node and explores as far deep as possible along each branch before backtracking
(bfs) breadth first search
algorithm starts at the root node and explores all of its neighbor nodes at the present depth prior to moving on to the nodes at the next depth level
(bds) bidirectional breadth first search
algorithm runs two simultaneous breadth first searches: one forward from the starting marker, and one backward from the ending marker, stopping once the two paths meet