Day4 . 707.设计链表

题目链接：https://leetcode.cn/problems/design-linked-list/

• 获取链表第index个节点的数值

   def get(self, index: int) -> int:
          if index < 0 or index >= self.size:
              return -1
          
          current = self.dummy_head.next
          #(0,index-1)
          for i in range(index):
              current = current.next
          
          return current.val 

• 在链表的最前面插入一个节点

  def addAtHead(self, val: int) -> None:
          self.dummy_head.next = ListNode(val,self.dummy_head.next)
          self.size += 1

• 在链表的最后面插入一个节点

  def addAtTail(self, val: int) -> None:
          current = self.dummy_head
          #判断下一个是否为NULL
          while current.next:
              current = current.next
          current.next = ListNode(val)
          self.size += 1

• 在链表第index个节点前面插入一个节点

  def addAtIndex(self, index: int, val: int) -> None:
          if index < 0 or index > self.size:
              return
          
          current = self.dummy_head
          #遍历到第index-1个节点
          for i in range(index):
              current = current.next
  
          current.next = ListNode(val,current.next)
          self.size += 1
  

• 删除链表的第index个节点

  def deleteAtIndex(self, index: int) -> None:
          if index < 0 or index >= self.size:
              return
      
          current = self.dummy_head
          for i in range(index):
              current = current.next
          current.next = current.next.next
          self.size -= 1

完整代码：

#
# @lc app=leetcode.cn id=707 lang=python3
#
# [707] 设计链表
#

# @lc code=start
class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

class MyLinkedList:

    def __init__(self):
        self.dummy_head = ListNode()
        self.size = 0

        
    
    def get(self, index: int) -> int:
        if index < 0 or index >= self.size:
            return -1
        
        current = self.dummy_head.next
        for i in range(index):
            current = current.next
        
        return current.val 

    def addAtHead(self, val: int) -> None:
        self.dummy_head.next = ListNode(val,self.dummy_head.next)
        self.size += 1

    def addAtTail(self, val: int) -> None:
        current = self.dummy_head
        while current.next:
            current = current.next
        current.next = ListNode(val)
        self.size += 1

    def addAtIndex(self, index: int, val: int) -> None:
        if index < 0 or index > self.size:
            return
        
        current = self.dummy_head

        for i in range(index):
            current = current.next
        current.next = ListNode(val,current.next)
        self.size += 1

    def deleteAtIndex(self, index: int) -> None:
        if index < 0 or index >= self.size:
            return
    
        current = self.dummy_head
        for i in range(index):
            current = current.next
        current.next = current.next.next
        self.size -= 1


# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)
# @lc code=end