[graph-tool] Why DFS `discoveres` the vertex, that it should not?
shpavel
shvets.pavel.srcc at gmail.com
Mon Mar 4 15:22:53 CET 2013
i have a very simple directed graph:
V0 -> V2
V1 -> V2
i use BFS and DFS algorithms starting from V0 and get different results from
`discover_vertex` function:
for BFS it does not discover V1, that is correct - there is no path from V0
to V1
but for DFS it does discover V1
output:
directed graph
0 2 BFS visited 2 // correct
0 2 1 DFS visited 3 // wrong
undirected graph
0 2 1 BFS visited 3 // correct
0 2 1 DFS visited 3 // correct
code:
import graph_tool.all as gt
class BFSCheck(gt.BFSVisitor):
def __init__(self):
self.visited = 0
def discover_vertex(self, u):
self.visited += 1
print u,
class DFSCheck(gt.DFSVisitor):
def __init__(self):
self.visited = 0
def discover_vertex(self, u):
self.visited += 1
print u,
def Cmp(graph):
v0 = graph.add_vertex()
v1 = graph.add_vertex()
v2 = graph.add_vertex()
e0 = graph.add_edge(v0, v2)
e1 = graph.add_edge(v1, v2)
bfs_check = BFSCheck()
gt.bfs_search(graph, v0, bfs_check)
print "BFS visited %d" % bfs_check.visited
dfs_check = DFSCheck()
gt.dfs_search(graph, v0, dfs_check)
print "DFS visited %d" % dfs_check.visited
graph_u = gt.Graph(directed = False)
graph_d = gt.Graph(directed = True)
print "directed graph"
Cmp(graph_d)
print
print "undirected graph"
Cmp(graph_u)
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