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"""
====================
Breadth-first search
====================
Basic algorithms for breadth-first searching.
"""
__author__ = """\n""".join(['Aric Hagberg <hagberg@lanl.gov>'])
__all__ = ['bfs_edges', 'bfs_tree',
'bfs_predecessors', 'bfs_successors']
import networkx as nx
from collections import defaultdict
def bfs_edges(G,source):
"""Produce edges in a breadth-first-search starting at source."""
# Based on http://www.ics.uci.edu/~eppstein/PADS/BFS.py
# by D. Eppstein, July 2004.
visited=set([source])
stack = [(source,iter(G[source]))]
while stack:
parent,children = stack[0]
try:
child = next(children)
if child not in visited:
yield parent,child
visited.add(child)
stack.append((child,iter(G[child])))
except StopIteration:
stack.pop(0)
def bfs_tree(G, source):
"""Return directed tree of breadth-first-search from source."""
return nx.DiGraph(bfs_edges(G,source))
def bfs_predecessors(G, source):
"""Return dictionary of predecessors in breadth-first-search from source."""
return dict((t,s) for s,t in bfs_edges(G,source))
def bfs_successors(G, source):
"""Return dictionary of successors in breadth-first-search from source."""
d=defaultdict(list)
for s,t in bfs_edges(G,source):
d[s].append(t)
return dict(d)
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