recurisve depth first traversal

same but.. delay the pop of an item from the stack until all its neighbours have been processed, and we only push those one at a time.

topological sorting

In a directed graph we have edges from v to w which do not necessarily imply an edge from w to v.

then is a neighbor of v but not (necessarily) vice versa.

suppose edges indicate some dependency

we want an order of vertices that finishes with v but never containes any vertex unless all the things that depend on it occur earlier

this is a (reverse) topological sort

for this to work the graph must be acyclic. i.e., we cannot have a depends on v which depends on w which depends on a

it that condition is met a recursive depth first traversal can be used.3