python doubly linked list - insertAfter node

Question

Im creating a python class to implement a doubly linked list. I have a seperate class for the DLL node itself and a class for the list. This is my class for the DLL nodes: class DLLNode:

def __init__(self,element,nextnode=None,prevnode=None,):

    self._element = element
    self._next = nextnode
    self._prev = prevnode

I have a method called insertAfter(self,x,y) which inserts node y after the first occurence x. Which is this :

if self.size != 0:
        n = DLLNode(y)
        if self.head._element == x:
            n._next = self.head._next
            self.head._next._prev = n
            n._prev = self.head
            self.head._next = n
            self.size += 1

        elif self.tail._element == x:
            self.tail._next = n
            n._prev = self.tail
            n._next = None
            self.tail = n
            self.size += 1
        else:
            iterator = self.head._next
            while iterator._next is not None:
                if iterator._element == x:
                    n._next = iterator._next
                    iterator._next._prev = n
                    n._prev = iterator
                    iterator._next = n
                    self.size += 1
                else:
                    iterator = iterator._next

when i run this function however, the function loops forever, when i kill the function myself, the error refers back to the 4th last line iterator._next = n it doesnt say anything else which is why im confused. Would greatly appreciate any help :)

kvorobiev · Accepted Answer · 2017-10-20 15:04:54Z

1

In the loop

while iterator._next is not None:

in then branch you doesn't change iterator value. On every iteration both conditions iterator._next is not None (from while loop) and if iterator._element == x: are True (because iterator contain same value). And you get infinity loop. Try to add break at the end of then branch.

answered Oct 20, 2017 at 15:04

kvorobiev

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