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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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def max_distance(node, ancestors, distances, root_descendants):
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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"""
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best = distances[node]
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for ancestor in ancestors[node]:
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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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# 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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if ancestor not in distances:
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if best is None or distances[ancestor]+1 > best:
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best = distances[ancestor] + 1
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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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distances = {start: 0}
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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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distances[descendant] = distance
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new_lines.add(descendant)
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def nodes_by_distance(distances):
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"""Return a list of nodes sorted by distance"""
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node_list = distances.keys()
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node_list.sort(key=by_distance, reverse=True)
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def select_farthest(distances, common):
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"""Return the farthest common node, or None if no node qualifies."""
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node_list = nodes_by_distance(distances)
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for node in node_list:
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def all_descendants(descendants, start):
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"""Produce a set of all descendants of the start node.
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The input is a map of node->list of descendants for a graph encompassing
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if line not in descendants:
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for descendant in descendants[line]:
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if descendant in result:
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result.add(descendant)
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new_lines.add(descendant)
added
removed
bzrlib/graph.py
