# Copyright (c) 2007-2008 Pedro Matiello <pmatiello@gmail.com>

#

# Permission is hereby granted, free of charge, to any person

# obtaining a copy of this software and associated documentation

# files (the "Software"), to deal in the Software without

# restriction, including without limitation the rights to use,

# copy, modify, merge, publish, distribute, sublicense, and/or sell

# copies of the Software, and to permit persons to whom the

# Software is furnished to do so, subject to the following

# conditions:

# The above copyright notice and this permission notice shall be

# included in all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES

# OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT

# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,

# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

# OTHER DEALINGS IN THE SOFTWARE.

"""

Traversal algorithms for python-graph.

@sort: traversal

"""

# Minimal spanning tree

def traversal(graph, node, order):

	"""

	Graph traversal iterator.

	@type  node: node

	@param node: Node.

	@type  order: string

	@param order: traversal ordering. Possible values are:

		2. 'pre' - Preordering (default)

		1. 'post' - Postordering

	@rtype:  iterator

	@return: Traversal iterator.

	"""

	visited = {}

	if (order == 'pre'):

		pre = 1

		post = 0

	elif (order == 'post'):

		pre = 0

		post = 1

	for each in _dfs(graph, visited, node, pre, post):

		yield each

def _dfs(graph, visited, node, pre, post):

	"""

	Depht-first search subfunction for traversals.

	@type  graph: graph

	@param graph: Graph.

	@type  visited: dictionary

	@param visited: List of nodes (visited nodes are marked non-zero).

	@type  node: node

	@param node: Node to be explored by DFS.

	"""

	visited[node] = 1

	if (pre): yield node

	# Explore recursively the connected component

	for each in graph[node]:

		if (each not in visited):

			for other in _dfs(graph, visited, each, pre, post):

				yield other

	if (post): yield node