~bzr-pqm/bzr/bzr.dev

974.1.68 by Aaron Bentley
Added GPL notice
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# (C) 2005 Canonical
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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974.1.72 by Aaron Bentley
added all_descendants and node_distances, exception when root doesn't exist
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def max_distance(node, ancestors, distances, root_descendants):
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more cleanups, docs, sorting stuff
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    """Calculate the max distance to an ancestor.  
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    Return None if not all possible ancestors have known distances"""
974.1.59 by aaron.bentley at utoronto
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    best = None
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    if node in distances:
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        best = distances[node]
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    for ancestor in ancestors[node]:
974.1.72 by Aaron Bentley
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        # skip ancestors we will never traverse:
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        if root_descendants is not None and ancestor not in root_descendants:
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            continue
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        # An ancestor which is not listed in ancestors will never be in
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        # distances, so we pretend it never existed.
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        if ancestor not in ancestors:
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            continue
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        if ancestor not in distances:
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            return None
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        if best is None or distances[ancestor] > best:
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            best = distances[ancestor] + 1
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    return best
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974.1.72 by Aaron Bentley
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def node_distances(graph, ancestors, start, root_descendants=None):
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    """Produce a list of nodes, sorted by distance from a start node.
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    This is an algorithm devised by Aaron Bentley, because applying Dijkstra
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    backwards seemed too complicated.
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    For each node, we walk its descendants.  If all the descendant's ancestors
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    have a max-distance-to-start, (excluding ones that can never reach start),
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    we calculate their max-distance-to-start, and schedule their descendants.
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    So when a node's last parent acquires a distance, it will acquire a
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    distance on the next iteration.
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    Once we know the max distances for all nodes, we can return a list sorted
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    by distance, farthest first.
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    """
974.1.59 by aaron.bentley at utoronto
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    distances = {start: 0}
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    lines = set([start])
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    while len(lines) > 0:
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        new_lines = set()
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        for line in lines:
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            line_descendants = graph[line]
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            assert line not in line_descendants, "%s refers to itself" % line
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            for descendant in line_descendants:
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                distance = max_distance(descendant, ancestors, distances,
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                                        root_descendants)
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                if distance is None:
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                    continue
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                distances[descendant] = distance
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                new_lines.add(descendant)
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        lines = new_lines
974.1.72 by Aaron Bentley
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    return distances
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974.1.72 by Aaron Bentley
added all_descendants and node_distances, exception when root doesn't exist
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def farthest_nodes(graph, ancestors, start):
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    def by_distance(n):
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        return distances[n],n
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    distances = node_distances(graph, ancestors, start)
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    node_list = distances.keys()
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    node_list.sort(key=by_distance, reverse=True)
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    return node_list
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def all_descendants(descendants, start):
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    result = set()
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    lines = set([start])
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    while len(lines) > 0:
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        new_lines = set()
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        for line in lines:
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            if line not in descendants:
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                continue
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            for descendant in descendants[line]:
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                if descendant in result:
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                    continue
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                result.add(descendant)
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                new_lines.add(descendant)
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        lines = new_lines
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    return result