以下のためのトポロジカルソート Dは irected A環式 Gの raph(DAG)有向无环图をすべての有向エッジのUVため、uは順序でVの前に頂点そのような頂点の線形順序であること。グラフがDAGでない場合は、グラフのためのトポロジカルソートはできません。
from collections import defaultdict
class Graph:
def __init__(self,vertices):
self.graph = defaultdict(list)
self.V=vertices
def addEdge(self,u,v):
self.graph[u].append(v)
#the function to do Topological Sort
def topologicalSort(self):
#create a vector to store indegrees of all vertices
in_degree=[0]*(self.V)
for i in self.graph:
for j in self.graph[i]:
in_degree[j]+=1
# Create an queue and enqueue all vertices with indegree 0
queue=[]
for i in range(self.V):
if in_degree[i]==0:
queue.append(i)
#Initialize count of visited vertices
cnt=0
# Create a vector to store result (A topological ordering of the vertices)
top_order=[]
# One by one dequeue vertices from queue and enqueue adjacents if indegree of adjacent becomes 0
while queue:
u=queue.pop(0)
top_order.append(u)
for i in self.graph[u]:
in_degree[i]-=1
if in_degree[i]==0:
queue.append(i)
cnt+=1
if cnt!=self.V:
print("there exists a cycle in the graph")
else:
print(top_order)
g=Graph(6)
g.addEdge(5, 2)
g.addEdge(5, 0)
g.addEdge(4, 0)
g.addEdge(4, 1)
g.addEdge(2, 3)
g.addEdge(3, 1)
print("Following is a Topological Sort of the given graph")
g.topologicalSort()
でる:
所与のグラフのトポロジカルソートされた次の
[4、5、2、0、3、1]