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Assignment 6: Directed graphs

Implement all of the following:

  1. From the creative problems for directed graphs:

    • 33: Unique topological ordering.

    Design an algorithm to determine whether a digraph has a unique topological ordering. Hint: a digraph has a unique topological ordering if and only if there is a directed edge between each pair of consecutive vertices in the topological order (i.e., the digraph has a Hamiltonian path). If the digraph has multiple topological orderings, then a second topological order can be obtained by swapping a pair of consecutive vertices.

  2. From the web exercises for directed graphs:

    • 30: One-way street theorem

    Implement an algorithm to orient the edges in an undirected graph so that it is strongly connected. Robbins theorem asserts that this is possible if and only if the undirected graph is two-edge connected (no bridges). In this case, a solution is to run DFS and oriented all edges in the DFS tree away from the root and all of the remaining edges toward the root.

    • 34: Number of paths in a DAG

    Given a DAG and two distinguished vertices s and t, design a linear-time algorithm to compute the number of directed paths from s to t. Hint: topological sort.

    • 35: Path of length L in a DAG

    Given a DAG and two distinguished vertices s and t, design an algorithm to determine if there exists a path from s to t containing exactly L edges.

To save you some time, your repository contains most of the classes from the book that you will need, or might consider using.