3.6 Directed Acyclic Graphs and topological Ordering

If a directed graph has no cycles, it's called a Directed Acyclic Graph(DAG). DAGS can be used to implement dependencies or precedence relations and are widely used in Computer Science.For instance, we can have a set of tasks {1, 2, 3,…, n} to be performed, the condition being that for certain tasks i and j, i must be performed before j. Each task is represented by a node, and there is an edge from i to j if i must be performed before j.