[Data Structure] Graph: Topological Sort

A topological sort of a directed, acyclic graph produces a list of graph's vertices such that for every edge from a vertex X to a vertex Y, X comes before Y in the list. 

There can be more than one valid topoligcal sort. Again, the graph must be acyclic and riected in order to apply topological sorting. 

 

The time complexity and space complexity of topological sorting is O(|V| + |E|).