@@ -486,15 +486,10 @@ class MyLinkedList {
486486Python:
487487``` python
488488# 单链表
489- class Node (object ):
490- def __init__ (self x = 0 ):
491- self .val = x
492- self .next = None
493- 494- class MyLinkedList (object ):
489+ class MyLinkedList1 :
495490
496491 def __init__ (self
497- self .head = Node()
492+ self .dummy_head = Node()# 添加虚拟头指针,便于操作
498493 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
499494
500495 def get (self index ):
@@ -504,7 +499,7 @@ class MyLinkedList(object):
504499 """
505500 if index < 0 or index >= self .size:
506501 return - 1
507- cur = self .head .next
502+ cur = self .dummy_head .next
508503 while (index):
509504 cur = cur.next
510505 index -= 1
@@ -516,8 +511,8 @@ class MyLinkedList(object):
516511 :rtype: None
517512 """
518513 new_node = Node(val)
519- new_node.next = self .head .next
520- self .head .next = new_node
514+ new_node.next = self .dummy_head .next
515+ self .dummy_head .next = new_node
521516 self .size += 1
522517
523518 def addAtTail (self val ):
@@ -526,7 +521,7 @@ class MyLinkedList(object):
526521 :rtype: None
527522 """
528523 new_node = Node(val)
529- cur = self .head
524+ cur = self .dummy_head
530525 while (cur.next):
531526 cur = cur.next
532527 cur.next = new_node
@@ -548,12 +543,12 @@ class MyLinkedList(object):
548543 return
549544
550545 node = Node(val)
551- pre = self .head
546+ cur = self .dummy_head
552547 while (index):
553- pre = pre .next
548+ cur = cur .next
554549 index -= 1
555- node.next = pre .next
556- pre .next = node
550+ node.next = cur .next
551+ cur .next = node
557552 self .size += 1
558553
559554 def deleteAtIndex (self index ):
@@ -563,7 +558,7 @@ class MyLinkedList(object):
563558 """
564559 if index < 0 or index >= self .size:
565560 return
566- pre = self .head
561+ pre = self .dummy_head
567562 while (index):
568563 pre = pre.next
569564 index -= 1
@@ -574,11 +569,10 @@ class MyLinkedList(object):
574569# 相对于单链表, Node新增了prev属性
575570class Node :
576571
577- def __init__ (self val ):
572+ def __init__ (self val = 0 , next = None , prev = None ):
578573 self .val = val
579- self .prev = None
580- self .next = None
581- 574+ self .next = next
575+ self .prev = prev
582576
583577class MyLinkedList :
584578
@@ -601,6 +595,20 @@ class MyLinkedList:
601595 node = node.next
602596 return node
603597
598+ 599+ def _update (self prev : Node, next : Node, val : int ) -> None :
600+ """
601+ 更新节点
602+ :param prev: 相对于更新的前一个节点
603+ :param next: 相对于更新的后一个节点
604+ :param val: 要添加的节点值
605+ """
606+ # 计数累加
607+ self ._count += 1
608+ node = Node(val)
609+ prev.next, next .prev = node, node
610+ node.prev, node.next = prev, next
611+ 604612 def get (self index : int ) -> int :
605613 """
606614 Get the value of the index-th node in the linked list. If the index is invalid, return -1.
@@ -634,19 +642,6 @@ class MyLinkedList:
634642 node = self ._get_node(index)
635643 self ._update(node.prev, node, val)
636644
637- def _update (self prev : Node, next : Node, val : int ) -> None :
638- """
639- 更新节点
640- :param prev: 相对于更新的前一个节点
641- :param next: 相对于更新的后一个节点
642- :param val: 要添加的节点值
643- """
644- # 计数累加
645- self ._count += 1
646- node = Node(val)
647- prev.next, next .prev = node, node
648- node.prev, node.next = prev, next
649- 650645 def deleteAtIndex (self index : int ) -> None :
651646 """
652647 Delete the index-th node in the linked list, if the index is valid.
@@ -656,6 +651,16 @@ class MyLinkedList:
656651 # 计数-1
657652 self ._count -= 1
658653 node.prev.next, node.next.prev = node.next, node.prev
654+ 655+ 656+ 657+ # Your MyLinkedList object will be instantiated and called as such:
658+ # obj = MyLinkedList()
659+ # param_1 = obj.get(index)
660+ # obj.addAtHead(val)
661+ # obj.addAtTail(val)
662+ # obj.addAtIndex(index,val)
663+ # obj.deleteAtIndex(index)
659664```
660665
661666Go:
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