LEETCODE 707. 设计链表

class ListNode:
    def __init__(self,val=0,next=None):
        self.val=val
        self.next=next

class MyLinkedList:

    def __init__(self):
        self.head=None
        self.size=0

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

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

    def addAtTail(self, val: int) -> None:
        if not self.head:
            self.addAtHead(val)
            return
        current_node=self.head
        while current_node.next:
            current_node=current_node.next
        current_node.next=ListNode(val)
        self.size+=1

    def addAtIndex(self, index: int, val: int) -> None:
        if index>self.size:
            return 
        if index<=0:
            self.addAtHead(val)
            return
        current_node=self.head
        for _ in range(index-1):
            current_node=current_node.next
        current_node.next=ListNode(val, current_node.next)
        self.size+=1
    def deleteAtIndex(self, index: int) -> None:
        if index<0 or index>=self.size:
            return
        self.size-=1
        
        if index==0:
            self.head=self.head.next
        else:
            current_node=self.head
            for _ in range(index-1):
                current_node=current_node.next
             
            current_node.next=current_node.next.next

# 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)