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Topological sorting with DFS. Another algorithm for sorting DAG nodes topologically. The idea is simple: perform 
a DFS and sort the nodes by inverse finish time. To easily get a linear running time, you can instead simply append 
nodes to your ordering as they receive their finish times in DFS. (See Listing 5-7.)
Tremaux’s algorithm. Like Ore’s algorithm, this is designed to be executed in person, while walking through a maze. 
The pattern traced by a person executing Tremaux’s algorithm is essentially the same as that of DFS. (See Chapter 5.)