Question

我在为部分代码设置索引时遇到了一些麻烦。关键功能是switch（）其他一切都很好。 switch函数的作用是获取给定索引处的节点，并将其与列表头部的节点进行切换。我是如此接近，但我无法弄清楚为什么当我运行测试功能（testswitch（））的第一种情况下它不会输出前两个节点，然后因为列表已被更改，第二个测试用例赢了' t由于TypeError而运行。任何帮助表示赞赏

"""
Creates and returns a linked list containing all of the elements
of the Python-style list parameter.
"""

def createList(plist):

    myList = None 
    for index in range(len(plist)-1, -1, -1):
        myList = insertValueHead(myList, plist[index])
    return myList

'''
Creates a string representation of the values in the linked list such as:
5->6->9->14.
'''

def listString(linkedList):


      ptr = linkedList
      str1 = ''
      while ptr != None:
        str1 += str(ptr['data'])
        ptr = ptr['next']
        if ptr != None:
          str1 += "->"
      str1 = str1
      return str1


'''
Inserts a new node containing the value "value" to the head of the list.
LinkedList is the head of the list to be added to
Value is the data to be stored in the node
'''

def insertValueHead(myList, value):

    newnode = {}
    newnode["data"] = value
    #set the next pointer of this new node to the head of the list, linkedList
    #newnode is now the head of the list 
    newnode["next"] = myList
    return newnode

def nthNode(myList, index):

    ptr = myList
    count = 0
    if index < 0:
        return None
    while ptr != None and count < index:
        ptr = ptr['next']
        count += 1
    return ptr

def switch(myList, index):

    newnode = {}
    newnode['data'] = 0
    newnode['next'] = None
    temphead = myList
    head = myList
    head = head['next']
    if index != 0:
        output = myList
    else:
        output = newnode
    prev, ptr = None, myList
    while ptr != None and index >0:
        prev = ptr
        ptr = ptr['next']
        index = index - 1
    if index > 0:
        print ('Index out of range')
    temphead['next'] = ptr['next']
    ptr['next'] = head
    prev['next'] = temphead
    print ptr['data']
    return output



def testSwitch():

    #test code to ensure that switch() is working correctly.
    myList = createList([10, 20, 30, 40, 50, 60])
    print "The initial list", listString(myList)
    myList = switch(myList, 2)
    print "Switching the head and the 30.  Resulting list is ", listString(myList)
    myList = switch(myList, 5)
    print "Switching the head and the 60.  Resuling list is ", listString(myList)
    myList = switch(myList, 29)  #should result in an error   
testSwitch()

这是追溯

Traceback (most recent call last):
  File "C:/Users/Hassan/Desktop/Python/assignment4.py", line 122, in <module>
    testSwitch()
  File "C:/Users/Hassan/Desktop/Python/assignment4.py", line 119, in testSwitch
    myList = switch(myList, 5)
  File "C:/Users/Hassan/Desktop/Python/assignment4.py", line 105, in switch
    temphead['next'] = ptr['next']
TypeError: 'NoneType' object has no attribute '__getitem__'

索引链表中的问题

0 个答案: