[英]Self-defined Dijkstra's algorithm in Python
I can successfully ran the codes that are not in a function format.我可以成功运行非函数格式的代码。 However, once I packaged everything into a function.然而,一旦我将所有东西都打包成一个函数。 I will receive an error.我会收到一个错误。 The data is as following:数据如下:
# A
graph_a = {}
graph_a['s'] = {}
graph_a['a'] = {}
graph_a['b'] = {}
graph_a['c'] = {}
graph_a['d'] = {}
graph_a['f'] = {}
graph_a['s']['a'] = 2
graph_a['s']['b'] = 5
graph_a['a']['b'] = 8
graph_a['a']['d'] = 7
graph_a['b']['d'] = 2
graph_a['b']['c'] = 4
graph_a['c']['d'] = 6
graph_a['c']['f'] = 3
graph_a['d']['f'] = 1
cost_a = {}
cost_a['a'] = 2
cost_a['b'] = 5
cost_a['f'] = float('inf')
cost_a['c'] = float('inf')
cost_a['d'] = float('inf')
parent_a = {}
parent_a['a'] = 's'
parent_a['b'] = 's'
parent_a['c'] = None
parent_a['d'] = None
parent_a['f'] = None
I also defined the lowest cost node function to find the lowest cost node in the cost in each iteration.我还定义了最低成本节点函数,以在每次迭代的成本中找到成本最低的节点。
searched = []
def lowestcostnode(x):
lowestnode = None
lowestcost = float('inf')
for node in x:
if x[node] < lowestcost and node not in searched:
lowestcost = x[node]
lowestnode = node
return lowestnode
I can get the results successfully via:我可以通过以下方式成功获得结果:
searched = []
node = lowestcostnode(cost_a)
while node is not None:
currentcost = cost_a[node]
neighbors = graph_a[node]
for n in neighbors:
if cost_a[n] > currentcost + neighbors[n]:
cost_a[n] = currentcost + neighbors[n]
parent_a[n] = node
searched.append(node)
node = lowestcostnode(cost_a)
The result is as:结果如下:
cost_a
{'a': 2, 'b': 5, 'f': 8, 'c': 9, 'd': 7}
But once I tried to packed the codes into a function, I got error message:但是一旦我尝试将代码打包到一个函数中,我就会收到错误消息:
def dijkstra(graph, parent, cost):
searched = []
node = lowestcostnode(cost)
while node is not None:
currentcost = cost[node]
neighbors = graph[node]
for n in neighbors:
if cost[n] > currentcost + neighbors[n]:
cost[n] = currentcost + neighbors[n]
parent[n] = node
searched.append(node)
node = lowestcostnode(cost)
print('parent as:', parent)
print('cost as:', cost)
return parent, cost
The error will be:错误将是:
dijkstra(graph_a, cost_a, parent_a)
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-57-00f1df255994> in <module>
----> 1 dijkstra(graph, parent, cost)
<ipython-input-56-517377fe9acb> in dijkstra(graph, parent, cost)
12 def dijkstra(graph, parent, cost):
13 searched = []
---> 14 node = lowestcostnode(cost)
15 while node is not None:
16 currentcost = cost[node]
<ipython-input-56-517377fe9acb> in lowestcostnode(x)
5 lowestcost = float('inf')
6 for node in x:
----> 7 if x[node] < lowestcost and node not in searched:
8 lowestcost = x[node]
9 lowestnode = node
NameError: name 'searched' is not defined
However, I already defined the searched one line before calling the lowestcostnode function.但是,在调用最低成本节点函数之前,我已经定义了搜索到的一行。
Thank you in advance for your help.预先感谢您的帮助。
You are calling: dijkstra(graph_a, cost_a, parent_a) but based on your function definition I would expect: dijkstra(graph_a, parent_a, cost_a)您正在调用:dijkstra(graph_a, cost_a, parent_a) 但根据您的函数定义,我期望:dijkstra(graph_a, parent_a, cost_a)
Does this fix your problem?这能解决您的问题吗?
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