portage.util.digraph: Add get_cycles() and its helpers shortest_path() and bfs()

diff --git a/pym/portage/util/digraph.py b/pym/portage/util/digraph.py
index 4502ed5827e83b642bc0a379dee8c76e03cec22c..9852bf8595d7e4a1e9a02d7e2bd4f90da6523129 100644 (file)
--- a/pym/portage/util/digraph.py
+++ b/pym/portage/util/digraph.py
@@ -3,6 +3,7 @@
 
 __all__ = ['digraph']
 
+from collections import deque
 from portage.util import writemsg
 
 class digraph(object):
@@ -274,6 +275,40 @@ class digraph(object):
                        for child, priorities in self.nodes[node][0].items():
                                output("  %s (%s)\n" % (child, priorities[-1],))
 
+       def bfs(self, start, ignore_priority=None):
+           queue, enqueued = deque([(None, start)]), set([start])
+           while queue:
+               parent, n = queue.popleft()
+               yield parent, n
+               new = set(self.child_nodes(n, ignore_priority)) - enqueued
+               enqueued |= new
+               queue.extend([(n, child) for child in new])
+
+       def shortest_path(self, start, end, ignore_priority=None):
+           paths = {None: []}
+           for parent, child in self.bfs(start, ignore_priority):
+               paths[child] = paths[parent] + [child]
+               if child == end:
+                   return paths[child]
+           return []
+
+       def get_cycles(self, ignore_priority=None, max_length=None):
+               """
+               Returns all cycles that have at most length 'max_length'.
+               If 'max_length' is 'None', all cycles are returned.
+               """
+               all_cycles = []
+               for node in self.nodes:
+                       shortest_path = None
+                       for child in self.child_nodes(node, ignore_priority):
+                               path = self.shortest_path(child, node, ignore_priority)
+                               if not shortest_path or len(shortest_path) > len(path):
+                                       shortest_path = path
+                       if shortest_path:
+                               if not max_length or len(shortest_path) <= max_length:
+                                       all_cycles.append(shortest_path)
+               return all_cycles
+
        # Backward compatibility
        addnode = add
        allnodes = all_nodes