# Copyright (c) 2007-2009 Pedro Matiello <pmatiello@gmail.com>
#
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"""
Sorting algorithms.

@sort: topological_sorting
"""


# Imports
from pygraph.algorithms.searching import depth_first_search

# Topological sorting
def topological_sorting(graph):
    """
    Topological sorting.

    @attention: Topological sorting is meaningful only for directed acyclic graphs.

    @type  graph: digraph
    @param graph: Graph.

    @rtype:  list
    @return: Topological sorting for the graph.
    """
    # The topological sorting of a DAG is equivalent to its reverse postordering.
    order = depth_first_search(graph)[2]
    order.reverse()
    return order
