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Doubly Linked List

Insert at beginning​

def insertAtBeginning(head, x):
    t = Node(x)
    if head:
        head.prev = t
    t.next = head
    return t

Insert at end​

def insertAtEnd(head, x):
    t = Node(x)
    if not head:
        return t
    curr = head
    while curr.next:
        curr = curr.next
    curr.next = t
    t.prev = curr
    return head

Delete first​

def delFirst(head):
    if head == None or head.next == None:
        return None
    head = head.next
    head.prev = None
    return head

Delete last​

def delLast(head):
    if head == None or head.next == None:
        return None
    curr = head
    while curr.next.next:
        curr = curr.next
    curr.next = None
    return head