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代码随想录70期day3

news 2025/9/6 7:21:18

203. Remove Linked List Elements

需要虚拟节点

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:def removeElements(self, head: Optional[ListNode], val: int) -> Optional[ListNode]:dummy_head = ListNode(next = head)# iterate the whole list to remove the node whoose value equals to the number of valcurrent = dummy_headwhile current.next:if current.next.val == val:current.next = current.next.nextelse:current = current.next return dummy_head.next

707

Single linklists

# Single Linklist
class ListNode:def __init__(self,val = 0,next=None):self.val = valself.next = nextclass MyLinkedList:def __init__(self):self.dummy_head = ListNode()self.size = 0def get(self,index:int) -> int:if index < 0 or index >= self.size:return -1current = self.dummy_head.next for i in range(index):current = current.index return current.indexdef addAtHead(self,val:int) ->None:self.dummy_head.next = ListNode(val,self.dummy_head.next)self.size += 1def addAtTail(self,val:int)->None:current = self.dummy_headwhile current.next:current = current.next current.next = ListNode(val)self.size += 1def addAtIndex(self,index:int,val:int) -> None:if index < 0 or index >self.size:return current = self.dummy_headfor i in range(index):current = current.next current.next = ListNode(val,current.next)self.size += 1def deleteAtIndex(self,index:int) ->None:if index < 0 or index >= self.size:return current = self.dummy_headfor i in range(index):current = current.next current.next = current.next.nextself.size -=1

Double Linklist

class ListNode:def __init__(self,val =0,prev = None,next = None):self.val = val self.prev = prev self.next = next class MyLinkedList:def __init__(self):self.head = None self.tail = None self.size = 0def get(self,index:int)->int:if index < 0 or index >= self.size:return -1if index < self.size//2:current = self.headfor i in range(index):current = current.nextelse:current = self.tail for i range(self.size - index - 1):current = current.prev return current.val def addAtHead(self,val:int)->None:new_node =ListNode(val,None,self.head)if self.head:self.head.prev = new_node else:self.tail = new_node self.head = new_node self.size +=1def addAtTail(self,val:int)->None:new_node = ListNode(val,self.tail,None)if self.tail:self.tail.next = new_node else:self.head = new_nodeself.tail = new_node self.size += 1def addAtIndex(self,index:int,val:int)->None:if index < 0 or index > self.size:return if index == 0:self.addAtHead(val)elif index == self.size:self.addAtTail(val)else:if index <self.size //2:current = self.head for i in range(index - 1):current = current.next else:current = self.tail for i in range(self.size-index):current = current.prev new_node = ListNode(val,current,current.next)current.next.prev = new_node current.next = new_node self.size +=1 def deleteAtIndex(self,index:int)->None:if index < 0 or index >=self.size:return if index == 0:self.head == self.head.next if self.head:self.head.prev = None else:self.tail = None elif index == self.size -1:self.tail = self.tail.prev if self.tail:self.tail.next = None else:self.head = None else:if index < self.size//2:current = self.head for i in range(index):current = current.next else:current = self.tail for i in range(self.size-index-1):current = current.prev current.prev.next = current.next current.next.prev = current.prev self.size -=1

206

# Two pointer version
class Solution:def reverseList(self,head:ListNode)->ListNode:cur = head pre = None while cur:temp  = cur.next cur.next = pre pre = cur cur = temp return pre# Recursive versionclass Solution:def reverseList(self,head:ListNode)->ListNode:return self.reverse(head,None)def reverse(self,cur:ListNode,pre:ListNode)->ListNode:if cur == None:return pre temp = cur.nextcur.next = prereturn self.reverse(temp,cur)