Python 判断 有向图 是否有环的实例讲解

import numpyfrom numpy import *def dfs( v ): vis[v] = -1 flag = 0 for i in range(n): # print (a[v][i],'---', vis[i] ) if a[v][i] != 0 and vis[i] != -1:  dfs(i)  vis[i] = 1 else:  pass if a[v][i] != 0 and vis[i] == -1:  print ('Yes, there is A loop in this network/n')  global swi  swi = True  exit()  return  # break else:  pass print ('s = 0') return Falseglobal swiswi = False'''===装载数据'''edges = numpy.loadtxt('9_nodes_with_r_edge_8_to_3.txt')# edges = [ int(i) for i in edges]bian = int(shape(edges)[0]) - 1print (bian,'edges in the network /n')print (shape(edges),'/n')n = int( edges[0][1] )c = int( edges[0][0] )# n, c = input().split()# n = int(n)# c = int(c)a = [([0] * n) for i in range(n)]vis = [0] * cfor i in range(1, c+1): s, t = edges[i][0:2] # print (s,' - ', t ) '''GO_OBO文件则 s, t 不需要 -1 ''' s = int(s) - 1 t = int(t) - 1 # s = int(s) # t = int(t) a[s][t] = 1# print (a)# print (vis)dfs(0)# print (swi)if not swi: print('No loop, DAG - DAG - DAG')