# Copyright (c) 2007-2008 Pedro Matiello <pmatiello@gmail.com>
#
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# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
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# copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following
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"""
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