【发布时间】：2016-01-30 01:11:01
【问题描述】：
我正在尝试使用 dfs 搜索在有向图中找到一个循环。我正在从包含顶点所有邻居的文本文件中读取文件。每当我调用 cycle_exists 方法时，我都会得到全部错误，所以答案永远不会改变。
Vertex.py
"""
__version__ = 'October 2015'
Vertex class reads in our graph and
performs a depth first search on it
and performs the transitive closure operation.
Vertex class also checks for cycles in our graph.
"""
import sys
class Graph:
def __init__(self):
"""
Initialize the variable used in Graph
"""
self.dfsPaths = [] #list for dfsPaths
self.VertexList = {} #list for adjacent vertices
def readInputGraph(self, inputFile):
"""
Reads specified input file and stores in
adjacency list
:param inputFile: file to be rad in
:return: the VertexList
"""
file = open(inputFile, 'r') #open the file and read it
for line in file: #for each element in the file
(vertex,val) = line.split() #vertex gets first value in the line, val gets second
if vertex not in self.VertexList: #if vertex not in VertexList
self.VertexList[vertex] = set([val]) #add adjacent pairs
else: #else
self.VertexList.get(vertex).add(val) #add the values
for i in list(self.VertexList.keys()): #for each element in the list of the vertex keys
for j in self.VertexList[i]: # for each vertex that's in i
if j not in self.VertexList: #if j is not in the vertex list
self.VertexList[j] = set() #we add it to the vertex list
return self.VertexList #return list of adjacent vertices
def dfsSearch(self, graph, start, end, path = []):
"""
Performs a depth first search on
the graph that is read in from the file
:param graph: the graph that we are performing the search on
:param start: the starting vertex
:param end: the target vertex
:param path: a list of the paths
:return: the paths from the search
"""
path = path + [start] #path
if start == end: #if the start element and end element are the same
return [path] #return the list of paths
if start not in graph: #if the start element is not in the graph
print( 'Not Found')#prints out not found
return [] #return an empty list
paths = [] #path list
for node in graph[start]: #for node in the graph
if node not in path: #if not in the path
newpaths = self.dfsSearch(graph, node, end, path) #new paths we found
for newpath in newpaths: #for each new path in the list of new paths
paths.append(newpath) #add the new path to our list of paths
paths.sort() #sort our paths
self.cycle_exists(graph)
#print(self.cycle_exists(graph))
return paths #return our paths
def cycle_exists(self, graph): # -graph is our graph.
color = { node : "white" for node in graph} #color all nodes white to begin with
found_cycle = False # found_cycle set to false
for node in graph: # for each node in graph.
if color[node]:#if the color[node] is white
self.dfs_visit(graph, node, color, found_cycle) #we call the dfs_visit method
if found_cycle:#if a cycle is found
found_cycle = True
break#break
return found_cycle #return the true or false
def dfs_visit(self,graph, node, color, found_cycle):
#print(color)
if found_cycle: # if a cycle is found return to the cycle_exists method
return
color[node] = "gray"#else color the node gray
for neighbor in graph[node]: #for every neighbor in the graph of the node
if color[neighbor] == "gray": #If neighbor is gray
found_cycle = True # then a cycle exists.
return
if color[neighbor] == "white": #if the neighbor is white
#print(color[neighbor])
self.dfs_visit(graph, neighbor, color, found_cycle)# call dfs_visit .
color[node] = "black"# color the original node black
GraphDriver.py 从顶点导入 * 导入系统
class GraphDriver:
def __init__(self):
self.graph = Graph()
def main():
graph = Graph()
inFile = sys.argv[1]
d = graph.readInputGraph(inFile)
userInput = input("Enter a source and destination:")
dog = userInput.split(" ", -1)
for path in graph.dfsSearch(d, dog[0], dog[1]):
print(path)
if __name__ == '__main__':
main()
输入.txt 0 1 0 6 1 2 1 5 2 3 2 4 4 3 4 0 5 4 6 5
【问题讨论】：