Sept. 7, 2015, 4:12 p.m. by Rosalind Team
Find a topological ordering of a directed acyclic graph.
Given: The adjacency list of a graph (with nodes represented by integers).
Return: A topological ordering of this graph.
1 -> 2 2 -> 3 4 -> 2 5 -> 3
1, 4, 5, 2, 3