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"""
Search algorithms.
"""
__authors__ = """Eben Kenah\nAric Hagberg (hagberg@lanl.gov)"""
# Copyright (C) 2004-2008 by
# Aric Hagberg <hagberg@lanl.gov>
# Dan Schult <dschult@colgate.edu>
# Pieter Swart <swart@lanl.gov>
# All rights reserved.
# BSD license.
__all__ = ['dfs_preorder', 'dfs_postorder',
'dfs_predecessor', 'dfs_successor', 'dfs_tree']
import networkx
def dfs_preorder(G,source=None,reverse_graph=False):
"""Return list of nodes connected to source in depth-first-search preorder.
Traverse the graph G with depth-first-search from source.
Non-recursive algorithm.
"""
if source is None:
nlist=G.nodes() # process entire graph
else:
nlist=[source] # only process component with source
if reverse_graph:
try:
neighbors=G.predecessors_iter
except:
neighbors=G.neighbors_iter
else:
neighbors=G.neighbors_iter
seen={} # nodes seen
pre=[] # list of nodes in a DFS preorder
for source in nlist:
if source in seen: continue
queue=[source] # use as LIFO queue
while queue:
v=queue[-1]
if v not in seen:
pre.append(v)
seen[v]=True
done=1
for w in neighbors(v):
if w not in seen:
queue.append(w)
done=0
break
if done==1:
queue.pop()
return pre
def dfs_postorder(G,source=None,reverse_graph=False):
"""
Return list of nodes connected to source in depth-first-search postorder.
Traverse the graph G with depth-first-search from source.
Non-recursive algorithm.
"""
if source is None:
nlist=G.nodes() # process entire graph
else:
nlist=[source] # only process component with source
if reverse_graph==True:
try:
neighbors=G.predecessors_iter
except:
neighbors=G.neighbors_iter
else:
neighbors=G.neighbors_iter
seen={} # nodes seen
post=[] # list of nodes in a DFS postorder
for source in nlist:
if source in seen: continue
queue=[source] # use as LIFO queue
while queue:
v=queue[-1]
if v not in seen:
seen[v]=True
done=1
for w in neighbors(v):
if w not in seen:
queue.append(w)
done=0
break
if done==1:
post.append(v)
queue.pop()
return post
def dfs_tree(G,source=None,reverse_graph=False):
"""Return directed graph (tree) of depth-first-search with root at source.
If the graph is disconnected, return a disconnected graph (forest).
"""
succ=dfs_successor(G,source=source,reverse_graph=reverse_graph)
return networkx.DiGraph(succ)
def dfs_predecessor(G,source=None,reverse_graph=False):
"""
Return predecessors of depth-first-search with root at source.
"""
if source is None:
nlist=G.nodes() # process entire graph
else:
nlist=[source] # only process component with source
if reverse_graph==True:
try:
neighbors=G.predecessors_iter
except:
neighbors=G.neighbors_iter
else:
neighbors=G.neighbors_iter
seen={} # nodes seen
pred={}
for source in nlist:
if source in seen: continue
queue=[source] # use as LIFO queue
pred[source]=[]
while queue:
v=queue[-1]
if v not in seen:
seen[v]=True
done=1
for w in neighbors(v):
if w not in seen:
queue.append(w)
pred[w]=[v] # Each node has at most one predecessor
done=0
break
if done==1:
queue.pop()
return pred
def dfs_successor(G,source=None,reverse_graph=False):
"""
Return succesors of depth-first-search with root at source.
"""
if source is None:
nlist=G.nodes() # process entire graph
else:
nlist=[source] # only process component with source
if reverse_graph==True:
try:
neighbors=G.predecessors_iter
except:
neighbors=G.neighbors_iter
else:
neighbors=G.neighbors_iter
seen={} # nodes seen
succ={}
for source in nlist:
if source in seen: continue
queue=[source] # use as LIFO queue
while queue:
v=queue[-1]
if v not in seen:
seen[v]=True
succ[v]=[]
done=1
for w in neighbors(v):
if w not in seen:
queue.append(w)
succ[v].append(w)
done=0
break
if done==1:
queue.pop()
return succ
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