我正在尝试使用Tarjan算法确定有向图中的循环。此算法详细介绍于Tarjan在1972年9月发表的研究论文“枚举有向图的基本回路”中。我使用Python编写算法,并使用邻接链表来跟踪节点之间的关系。在下面的"G"中,节点0指向节点1,节点1指向节点4、6、7...等等。请参考以下图形可视化结果:。
Tarjan算法可以检测到以下环路:
G = [[1], [4, 6, 7], [4, 6, 7], [4, 6, 7], [2, 3], [2, 3], [5, 8], [5, 8], [], []]
N = len(G)
points = []
marked_stack = []
marked = [False for x in xrange(0,N)]
g = None
def tarjan(s, v, f):
global g
points.append(v)
marked_stack.append(v)
marked[v] = True
for w in G[v]:
if w < s:
G[v].pop(G[v].index(w))
elif w == s:
print points
f = True
elif marked[w] == False:
if f == g and f == False:
f = False
else:
f = True
tarjan(s, w, g)
g = f
if f == True:
u = marked_stack.pop()
while (u != v):
marked[u] = False
u = marked_stack.pop()
#v is now deleted from mark stacked, and has been called u
#unmark v
marked[u] = False
points.pop(points.index(v))
for i in xrange(0,N):
marked[i] = False
for i in xrange(0,N):
points = []
tarjan(i,i, False)
while (len(marked_stack) > 0):
u = marked_stack.pop()
marked[u] = False
Tarjan算法可以检测到以下环路:
我还使用了Tiernan算法,它(正确地)找到了额外的两个环:[2, 4]
[2, 4, 3, 6, 5]
[2, 4, 3, 7, 5]
[2, 6, 5]
[2, 6, 5, 3, 4]
[2, 7, 5]
[2, 7, 5, 3, 4]
[3, 7, 5]
我想知道为什么Tarjan会忽略这两个环。也许是我的代码有问题?[3,4]
[3,6,5]