Dijkstra - 最近鄰確定

Question

在Dijkstra的算法中，我對最近鄰居的決心不知所措。 我得到如下奇怪的結果首先這是我的網絡文件的內容，代表7個節點之間的距離：

http://pastebin.com/PUM5qT6D

（不包括第一列中的數字1-7）

現在我的代碼：

> infinity = 1000000 invalid_node = -1
> startNode = 0
> 
> #Values to assign to each node class Node:
>      distFromSource = infinity
>      previous = invalid_node
>      visited = False
> 
> #read in all network nodes
> #node = the distance values between nodes def network():
>     f = open ('network.txt', 'r')
>     theNetwork = [[int(node) for node in line.split(',')] for line in
> f.readlines()]
>     #print theNetwork
> 
>     return theNetwork
> 
> #for each node assign default values
> #populate table with default values def populateNodeTable():
>     nodeTable = []
>     index = 0
>     f = open('network.txt', 'r')
>     for line in f:
>       node = map(int, line.split(','))
>       nodeTable.append(Node())
>      
>       #print "The previous node is " ,nodeTable[index].previous
>       #print "The distance from source is " ,nodeTable[index].distFromSource
>       index +=1
>     nodeTable[startNode].distFromSource =
> 0
> 
>     return nodeTable
> 
> #find the nearest neighbour to a particular node def
> nearestNeighbour(nodeTable,
> theNetwork):
>      nearestNeighbour = []
>      nodeIndex = 0
>      for node in nodeTable:
>           if node != 0 and Node.visited == False:
>              nearestNeighbour.append(nodeIndex)
>              nodeIndex +=1
>      print nearestNeighbour
> 
>      return nearestNeighbour
> 
> def tentativeDistance (theNetwork,
> nodeTable, nearestNeighbour):
>     shortestPath = []
>     for nodeIndex in nearestNeighbour:
>          currentDistance = nearestNeighbour[] + startNode
>          print currentDistance
> ##         if currentDistance < Node.distFromSource:
> ##            theNetwork[Node].previous = nodeIndex
> ##            theNetwork[Node].length = nodeIndex
> ##            theNetwork[Node].visited = True;
> ##            shortestPath.append(indexNode)
> ##            nodeIndex +=1
> ##    print shortestPath
> 
> currentNode = startNode
> 
> if __name__ == "__main__":
>     nodeTable = populateNodeTable()
>     theNetwork = network()
>     nearestNeighbour(nodeTable, theNetwork)
>     tentativeDistance(theNetwork, nodeTable, nearestNeighbour)

所以，我試着查看網絡函數提供的值，在populateNodeTable函數中將所有節點設置為'visited = false'，然后通過查看前一個函數中提供的值來確定節點的最近鄰居，盡管我得到了此錯誤消息：

> Traceback (most recent call last):  
> File "C:\Documents and Settings\Harvey\Desktop\2dArray.py", line 77, in <module>
>     tentativeDistance(theNetwork, nodeTable, nearestNeighbour)   File
> "C:\Documents and Settings\Harvey\Desktop\2dArray.py", line 51, in tentativeDistance
>     for nodeIndex in nearestNeighbour: TypeError: 'function' object is not iterable

當我運行我的網絡功能時，我得到了這個輸出：

[[0, 2, 4, 1, 6, 0, 0], [2, 0, 0, 0, 5, 0, 0], [4, 0, 0, 0, 5, 5, 0], [1, 0, 0, 0, 1, 1, 0], [6, 5, 0, 1, 0, 5, 5], [0, 0, 5, 1, 5, 0, 0], [0, 0, 0, 0, 5, 0, 0]]

到目前為止，非常好 - 當我運行populateNodeTable函數和我的網絡函數時，我得到了這個輸出：

> The previous node is  -1 
  The distance from source is  1000000 # happens 7 times#
> 

另外，這很好 - 除了上述功能之外，執行myNeighbour函數后的輸出是：

[0, 1, 2, 3, 4, 5, 6]

這個輸出是錯誤的，是我的問題開始的地方

此外，當我運行我的所有代碼包括tentativeDistance時，我收到此錯誤：

> for nodeIndex in nearestNeighbour:
  TypeError: 'function' object is not iterable

我為這篇文章長篇大論而道歉，我很沮喪，我無法掌握似乎是基本的功能

Answer 1

您將方法nearestNeighbour傳遞給tentativeDistance而不是方法的結果。

Answer 2

這是問題所在

tentativeDistance(theNetwork, nodeTable, nearestNeighbour)

應該

 x = nearestNeighbour(nodeTable, theNetwork)
 tentativeDistance(theNetwork, nodeTable, x)

看一下錯誤，你會看到代碼試圖迭代一個不可迭代的對象。 這在Python for - in - syntax中是隱含的。

您可能還會考慮重命名變量名稱或函數名稱以避免混淆。 無論如何，這都是一個容易犯的錯誤。