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Update 0707.设计链表.md
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jianghongcheng
@ -485,172 +485,166 @@ class MyLinkedList {
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Python：
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```python
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# 单链表
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class MyLinkedList1:
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def __init__(self):
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self.dummy_head = Node()# 添加虚拟头指针，便于操作
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self.size = 0 # 设置一个链表长度的属性，便于后续操作，注意每次增和删的时候都要更新
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def get(self, index):
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"""
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:type index: int
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:rtype: int
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"""
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if index < 0 or index >= self.size:
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return -1
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cur = self.dummy_head.next
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while(index):
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cur = cur.next
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index -= 1
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return cur.val
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def addAtHead(self, val):
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"""
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:type val: int
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:rtype: None
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"""
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new_node = Node(val)
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new_node.next = self.dummy_head.next
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self.dummy_head.next = new_node
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self.size += 1
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def addAtTail(self, val):
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"""
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:type val: int
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:rtype: None
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"""
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new_node = Node(val)
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cur = self.dummy_head
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while(cur.next):
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cur = cur.next
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cur.next = new_node
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self.size += 1
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def addAtIndex(self, index, val):
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"""
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:type index: int
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:type val: int
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:rtype: None
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"""
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if index < 0:
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self.addAtHead(val)
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return
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elif index == self.size:
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self.addAtTail(val)
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return
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elif index > self.size:
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return
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node = Node(val)
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cur = self.dummy_head
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while(index):
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cur = cur.next
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index -= 1
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node.next = cur.next
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cur.next = node
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self.size += 1
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def deleteAtIndex(self, index):
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"""
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:type index: int
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:rtype: None
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"""
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if index < 0 or index >= self.size:
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return
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pre = self.dummy_head
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while(index):
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pre = pre.next
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index -= 1
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pre.next = pre.next.next
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self.size -= 1
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# 双链表
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# 相对于单链表, Node新增了prev属性
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class Node:
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def __init__(self, val=0, next = None, prev = None):
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（版本一）单链表法
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class ListNode:
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def __init__(self, val=0, next=None):
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self.val = val
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self.next = next
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self.prev = prev
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class MyLinkedList:
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def __init__(self):
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self._head, self._tail = Node(0), Node(0) # 虚拟节点
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self._head.next, self._tail.prev = self._tail, self._head
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self._count = 0 # 添加的节点数
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def _get_node(self, index: int) -> Node:
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# 当index小于_count//2时, 使用_head查找更快, 反之_tail更快
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if index >= self._count // 2:
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# 使用prev往前找
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node = self._tail
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for _ in range(self._count - index):
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node = node.prev
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else:
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# 使用next往后找
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node = self._head
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for _ in range(index + 1):
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node = node.next
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return node
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def _update(self, prev: Node, next: Node, val: int) -> None:
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"""
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更新节点
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:param prev: 相对于更新的前一个节点
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:param next: 相对于更新的后一个节点
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:param val: 要添加的节点值
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"""
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# 计数累加
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self._count += 1
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node = Node(val)
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prev.next, next.prev = node, node
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node.prev, node.next = prev, next
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self.dummy_head = ListNode()
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self.size = 0
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def get(self, index: int) -> int:
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"""
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Get the value of the index-th node in the linked list. If the index is invalid, return -1.
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"""
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if 0 <= index < self._count:
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node = self._get_node(index)
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return node.val
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else:
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if index < 0 or index >= self.size:
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return -1
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current = self.dummy_head.next
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for i in range(index):
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current = current.next
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return current.val
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def addAtHead(self, val: int) -> None:
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"""
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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.
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"""
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self._update(self._head, self._head.next, val)
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self.dummy_head.next = ListNode(val, self.dummy_head.next)
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self.size += 1
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def addAtTail(self, val: int) -> None:
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"""
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Append a node of value val to the last element of the linked list.
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"""
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self._update(self._tail.prev, self._tail, val)
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current = self.dummy_head
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while current.next:
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current = current.next
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current.next = ListNode(val)
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self.size += 1
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def addAtIndex(self, index: int, val: int) -> None:
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"""
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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.
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"""
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if index < 0:
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index = 0
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elif index > self._count:
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if index < 0 or index > self.size:
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return
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node = self._get_node(index)
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self._update(node.prev, node, val)
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current = self.dummy_head
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for i in range(index):
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current = current.next
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current.next = ListNode(val, current.next)
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self.size += 1
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def deleteAtIndex(self, index: int) -> None:
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"""
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Delete the index-th node in the linked list, if the index is valid.
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"""
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if 0 <= index < self._count:
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node = self._get_node(index)
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# 计数-1
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self._count -= 1
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node.prev.next, node.next.prev = node.next, node.prev
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if index < 0 or index >= self.size:
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return
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current = self.dummy_head
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for i in range(index):
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current = current.next
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current.next = current.next.next
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self.size -= 1
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# Your MyLinkedList object will be instantiated and called as such:
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# obj = MyLinkedList()
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# param_1 = obj.get(index)
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# obj.addAtHead(val)
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# obj.addAtTail(val)
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# obj.addAtIndex(index,val)
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# obj.deleteAtIndex(index)
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```
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```python
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（版本二）双链表法
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class ListNode:
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def __init__(self, val=0, prev=None, next=None):
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self.val = val
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self.prev = prev
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self.next = next
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class MyLinkedList:
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def __init__(self):
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self.head = None
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self.tail = None
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self.size = 0
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def get(self, index: int) -> int:
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if index < 0 or index >= self.size:
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return -1
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if index < self.size // 2:
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current = self.head
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for i in range(index):
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current = current.next
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else:
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current = self.tail
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for i in range(self.size - index - 1):
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current = current.prev
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return current.val
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def addAtHead(self, val: int) -> None:
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new_node = ListNode(val, None, self.head)
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if self.head:
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self.head.prev = new_node
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else:
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self.tail = new_node
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self.head = new_node
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self.size += 1
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def addAtTail(self, val: int) -> None:
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new_node = ListNode(val, self.tail, None)
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if self.tail:
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self.tail.next = new_node
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else:
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self.head = new_node
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self.tail = new_node
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self.size += 1
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def addAtIndex(self, index: int, val: int) -> None:
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if index < 0 or index > self.size:
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return
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if index == 0:
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self.addAtHead(val)
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elif index == self.size:
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self.addAtTail(val)
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else:
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if index < self.size // 2:
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current = self.head
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for i in range(index - 1):
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current = current.next
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else:
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current = self.tail
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for i in range(self.size - index):
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current = current.prev
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new_node = ListNode(val, current, current.next)
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current.next.prev = new_node
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current.next = new_node
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self.size += 1
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def deleteAtIndex(self, index: int) -> None:
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if index < 0 or index >= self.size:
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return
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if index == 0:
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self.head = self.head.next
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if self.head:
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self.head.prev = None
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else:
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self.tail = None
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elif index == self.size - 1:
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self.tail = self.tail.prev
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if self.tail:
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self.tail.next = None
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else:
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self.head = None
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else:
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if index < self.size // 2:
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current = self.head
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for i in range(index):
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current = current.next
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else:
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current = self.tail
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for i in range(self.size - index - 1):
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current = current.prev
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current.prev.next = current.next
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current.next.prev = current.prev
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self.size -= 1
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