Singly Linked List.py

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


classMyLinkedList:
def__init__(self):
"""
 Initialize your data structure here.
 """
self.len=0
self.head=None


defget(self, index: int) ->int:
"""
 Get the value of the index-th node in the linked list. If the index is invalid, return -1.
 """
ifindex>=self.len:
return-1
curr=self.head
for_inrange(index):
curr=curr.next
returncurr.val


defaddAtHead(self, val: int) ->None:
"""
 Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
 """
head=ListNode(val)
head.next=self.head
self.head=head
self.len+=1


defaddAtTail(self, val: int) ->None:
"""
 Append a node of value val to the last element of the linked list.
 """
self.addAtIndex(self.len, val)


defaddAtIndex(self, index: int, val: int) ->None:
"""
 Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted.
 """
ifindex==0:
self.addAtHead(val)
elifindex<=self.len:
node=ListNode(val)
curr=self.head
for_inrange(index-1):
curr=curr.next
node.next=curr.next
curr.next=node
self.len+=1


defdeleteAtIndex(self, index: int) ->None:
"""
 Delete the index-th node in the linked list, if the index is valid.
 """
ifindex==0andself.len>0:
self.head=self.head.next
self.len-=1
elifindex<self.len:
curr=self.head
for_inrange(index-1):
curr=curr.next
curr.next=curr.next.next
self.len-=1



# 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)