Deleting a node in Linked List in python

问题

To delete a node in a linked list, what is wrong with this implementation?:

def delete(self, val):
    tmp = self.head
    prev = None
    while tmp: 
        if val == tmp.data:
            self.size -= 1
            if prev==None: 
                self.head = self.head.next 
            else:
                prev.next = tmp.next 
        else:
            prev = tmp
            tmp = tmp.next

All the guides I've looked at say it should be:

def delete(self, data):
    tmp = self.head
    prev = None
    found = False 
    while tmp and not found:
        if data == tmp.data:
            found = True
        else:
            prev = tmp
            tmp = tmp.next
    if found:
        self.size -= 1
        if prev == None:
            self.head = self.head.next
        else:
            prev.next = tmp.next

but I can't figure out why the found is needed. Why is the found necessary? Why is this implementation more correct?

Additionally, I have the same trouble with search:

My implementation is:

def __contains__(self, data):
    tmp = self.head
    while tmp:
        if data == tmp.data:
            return True 
        else: 
            tmp = tmp.next
    return False

but the correct implementation is:

def __contains__(self, data):
        tmp = self.head
        found = False
        while tmp and not found:
            if data == tmp.data:
                found = True
            else: 
                tmp = tmp.next
        return found

回答1:

The deletes are identical as long as data is unique. So it is in general better, do separate looping through the list, from working on elements. It is more readable, and less nested. It would be still better, to give an error, if data is not found:

def delete(self, data):
    tmp = self.head
    prev = None
    while tmp:
        if data == tmp.data:
            break
        prev = tmp
        tmp = tmp.next
    else:
        raise ValueError('data not found')
    self.size -= 1
    if prev is None:
        self.head = tmp.next
    else:
        prev.next = tmp.next

来源：https://stackoverflow.com/questions/32124723/deleting-a-node-in-linked-list-in-python

标签

python

linked-list