class ListNode:
def __init__(self, val):
self.val = val
self.prev = None
self.next = None
class MyLinkedList:
def __init__(self):
self.left = ListNode(0)
self.right = ListNode(0)
self.left.next = self.right
self.right.prev = self.left
def get(self, index: int) -> int:
cur = self.left.next
while cur and index > 0:
cur = cur.next
index -= 1
if cur and cur != self.right and index == 0:
return cur.val
return -1
def addAtHead(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
def addAtTail(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
def addAtIndex(self, index: int, val: int) -> None:
next = self.left.next
while next and index > 0:
next = next.next
index -= 1
if next and index == 0:
node, prev = ListNode(val), next.prev
node.next, node.prev = next, prev
next.prev = node
prev.next = node
def deleteAtIndex(self, index: int) -> None:
node = self.left.next
while node and index > 0:
node = node.next
index -= 1
if node and node != self.right and index == 0:
node.prev.next = node.next
node.next.prev = node.prev