在无向图中基于DFS在周期或死角中查找和打印节点

问题描述

我在大学里做一个练习，必须写一个扩展的DFS算法。 基于DFS，我必须指定一个遍历无向连续图的过程，根据是循环的一部分还是死角对每个节点进行分类，并打印循环中或死角中的节点。 此过程必须应用于起始节点S所示的图。 The drawn graph

我有以下邻接列表：

'S' : ['A']
'A' : ['B','F']
'B' : ['C','H']
'C' : ['D','B']
'D' : ['C','E','G']
'E' : ['D','F']
'F' : ['A','E']
'G' : ['D']
'H' : ['B','I']
'I' : ['H']

我已将每个节点映射到以下数字：

0: S
1: A
2: B
3: C
4: D
5: E
6: F
7: G
8: H
9: I

这是我到目前为止编写的用于检测图中周期的代码（已编辑）：

# Python Program to detect cycle in an undirected graph 
from collections import defaultdict

visitedList = list()
nodes = set()
s = ''


# This class represents a undirected graph using adjacency list representation
class Graph:

    def __init__(self,vertexCount):
        self.V = vertexCount  # No. of vertices
        self.graph = defaultdict(list)  # default dictionary to store graph

    # function to add an edge to graph
    def addEdge(self,v,w):
        self.graph[v].append(w)  # Add w to v_s list
        self.graph[w].append(v)  # Add v to w_s list
        nodes.add(v)
        nodes.add(w)
        # print(self.graph)

    # A recursive function that uses visited[] and parent to detect
    # cycle in subgraph reachable from vertex v.
    def isCyclicUtil(self,visited,parent,cycle=list()):
        global s
        visited[v] = True
        visitedList.append(v)
        # Recur for all the vertices adjacent to this vertex
        for i in self.graph[v]:
            # If the node is not visited then recurse on it
            if not visited[i]:
                cycle.append(i)
                if self.isCyclicUtil(i,cycle):
                    return
            # If an adjacent vertex is visited and not parent of current vertex,# then there is a cycle
            elif parent != i:
                s = 'Nodes in a cycle: '
                s += ' '.join(str(v) for v in cycle)
                s += '\nNodes in a dead end: '
                s += ' '.join(str(v) for v in Diff(nodes,cycle))
                #return
                return True
        return cycle

    # Returns true if the graph contains a cycle,else false.
    def isCyclic(self):
        # Mark all the vertices as not visited
        visited = [False] * (self.V)
        cycle = list()
        # Call the recursive helper function to detect cycle in different 
        # DFS trees
        for i in range(self.V):
            if not visited[i]:  # Don't recur for u if it is already visited
                if self.isCyclicUtil(i,-1,cycle):
                    return True
        return False


def Diff(li1,li2):
    return list(list(set(li1) - set(li2)) + list(set(li2) - set(li1)))


# Driver code
# Create a graph with given adjacency list
S = 0
A = 1
B = 2
C = 3
D = 4
E = 5
F = 6
G = 7
H = 8
I = 9

g = Graph(10)

g.addEdge(S,A)
g.addEdge(A,B)
g.addEdge(B,C)
g.addEdge(B,H)
g.addEdge(C,D)
g.addEdge(D,E)
g.addEdge(D,G)
g.addEdge(E,F)
g.addEdge(F,A)
g.addEdge(H,I)


if g.isCyclic():
    print("Graph contains cycle")
    print(s)
else:
    print("Graph does not contain cycle")

'''
g = Graph(6)

g.addEdge(0,1)
g.addEdge(1,3)
g.addEdge(1,2)
g.addEdge(1,4)
g.addEdge(4,5)

if g.isCyclic():
    print("Graph contains cycle")
    print(s)
else:
    print("Graph does not contain cycle")
'''

这里仍然缺少的是打印循环中或死胡同中的节点。

解决方法

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