单向链表

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):if index < 0 or index >= self.size:return -1current = self.dummy_head.nextfor i in range(index):current = current.nextreturn current.valdef addAtHead(self, val):self.dummy_head.next = ListNode(val, self.dummy_head.next)self.size += 1def addAtTail(self, val):current = self.dummy_headwhile current.next:current = current.nextcurrent.next = ListNode(val)self.size += 1def addAtIndex(self, index, val):if index < 0 or index > self.size:returncurrent = self.dummy_headfor i in range(index):current = current.nextcurrent.next = ListNode(val, current.next)self.size += 1def deleteAtIndex(self, index):if index < 0 or index >= self.size:returncurrent = self.dummy_headfor i in range(index):current = current.nextcurrent.next = current.next.nextself.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)