添加 0707.设计链表 Python3版本

This commit is contained in:
pppig
2021-05-18 10:21:30 +08:00
committed by GitHub
parent ea0973c6e4
commit 632ec4bdd4

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@ -231,8 +231,166 @@ class MyLinkedList {
```
Python
```python3
# 单链表
class Node:
def __init__(self, val):
self.val = val
self.next = None
class MyLinkedList:
def __init__(self):
self._head = Node(0) # 虚拟头部节点
self._count = 0 # 添加的节点数
def get(self, index: int) -> int:
"""
Get the value of the index-th node in the linked list. If the index is invalid, return -1.
"""
if 0 <= index < self._count:
node = self._head
for _ in range(index + 1):
node = node.next
return node.val
else:
return -1
def addAtHead(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.
"""
self.addAtIndex(0, val)
def addAtTail(self, val: int) -> None:
"""
Append a node of value val to the last element of the linked list.
"""
self.addAtIndex(self._count, val)
def addAtIndex(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.
"""
if index < 0:
index = 0
elif index > self._count:
return
# 计数累加
self._count += 1
add_node = Node(val)
prev_node, current_node = None, self._head
for _ in range(index + 1):
prev_node, current_node = current_node, current_node.next
else:
prev_node.next, add_node.next = add_node, current_node
def deleteAtIndex(self, index: int) -> None:
"""
Delete the index-th node in the linked list, if the index is valid.
"""
if 0 <= index < self._count:
# 计数-1
self._count -= 1
prev_node, current_node = None, self._head
for _ in range(index + 1):
prev_node, current_node = current_node, current_node.next
else:
prev_node.next, current_node.next = current_node.next, None
# 双链表
# 相对于单链表, Node新增了prev属性
class Node:
def __init__(self, val):
self.val = val
self.prev = None
self.next = None
class MyLinkedList:
def __init__(self):
self._head, self._tail = Node(0), Node(0) # 虚拟节点
self._head.next, self._tail.prev = self._tail, self._head
self._count = 0 # 添加的节点数
def _get_node(self, index: int) -> Node:
# 当index小于_count//2时, 使用_head查找更快, 反之_tail更快
if index >= self._count // 2:
# 使用prev往前找
node = self._tail
for _ in range(self._count - index):
node = node.prev
else:
# 使用next往后找
node = self._head
for _ in range(index + 1):
node = node.next
return node
def get(self, index: int) -> int:
"""
Get the value of the index-th node in the linked list. If the index is invalid, return -1.
"""
if 0 <= index < self._count:
node = self._get_node(index)
return node.val
else:
return -1
def addAtHead(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.
"""
self._update(self._head, self._head.next, val)
def addAtTail(self, val: int) -> None:
"""
Append a node of value val to the last element of the linked list.
"""
self._update(self._tail.prev, self._tail, val)
def addAtIndex(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.
"""
if index < 0:
index = 0
elif index > self._count:
return
node = self._get_node(index)
self._update(node.prev, node, val)
def _update(self, prev: Node, next: Node, val: int) -> None:
"""
更新节点
:param prev: 相对于更新的前一个节点
:param next: 相对于更新的后一个节点
:param val: 要添加的节点值
"""
# 计数累加
self._count += 1
node = Node(val)
prev.next, next.prev = node, node
node.prev, node.next = prev, next
def deleteAtIndex(self, index: int) -> None:
"""
Delete the index-th node in the linked list, if the index is valid.
"""
if 0 <= index < self._count:
node = self._get_node(index)
# 计数-1
self._count -= 1
node.prev.next, node.next.prev = node.next, node.prev
```
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