0707-design-linked-list.py

classListNode:
def__init__(self, val):
self.val=val
self.prev=None
self.next=None

classMyLinkedList:

def__init__(self):
self.left=ListNode(0)
self.right=ListNode(0)
self.left.next=self.right
self.right.prev=self.left

defget(self, index: int) ->int:
cur=self.left.next
whilecurandindex>0:
cur=cur.next
index-=1

ifcurandcur!=self.rightandindex==0:
returncur.val
return-1

defaddAtHead(self, val: int) ->None:
node, prev, next=ListNode(val), self.left, self.left.next
node.next, node.prev=next, prev
next.prev=node
prev.next=node

defaddAtTail(self, val: int) ->None:
node, prev, next=ListNode(val), self.right.prev, self.right
node.next, node.prev=next, prev
next.prev=node
prev.next=node

defaddAtIndex(self, index: int, val: int) ->None:
next=self.left.next
whilenextandindex>0:
next=next.next
index-=1

ifnextandindex==0:
node, prev=ListNode(val), next.prev
node.next, node.prev=next, prev
next.prev=node
prev.next=node


defdeleteAtIndex(self, index: int) ->None:
node=self.left.next
whilenodeandindex>0:
node=node.next
index-=1

ifnodeandnode!=self.rightandindex==0:
node.prev.next=node.next
node.next.prev=node.prev


# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)