00011

力扣707——单列表

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

class MyLinkedList(object):

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

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

    def addAtHead(self, val):
        self.dummy_head.next = ListNode(val, self.dummy_head.next)
        self.size += 1
        

    def addAtTail(self, val):
        cur = self.dummy_head
        for i in range(self.size):
            cur = cur.next
        cur.next = ListNode(val)
        self.size += 1
        

    def addAtIndex(self, index, val):
        if index <= self.size:
            cur = self.dummy_head
            for i in range(index):
                cur = cur.next
            cur.next = ListNode(val, cur.next) 
        else:
            return
        self.size += 1
        

    def deleteAtIndex(self, index):
        if index >= 0 and index < self.size:
            cur = self.dummy_head
            for i in range(index):
                cur = cur.next
            cur.next = cur.next.next
            self.size -= 1
        else:
            return