707.Design-Linked-List.py

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

class MyLinkedList:

    def __init__(self):
        self.head = ListNode(0)  # dummy header
        self.size = 0  # size of the linked list

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

    def addAtTail(self, val: int) -> None:
        cur = self.head
        new_node = ListNode(val)
        while cur.next:
            cur = cur.next
        cur.next = new_node
        self.size += 1
        
    def addAtIndex(self, index: int, val: int) -> None:
        if index == self.size:
            self.addAtTail(val)
        elif index > self.size or index < 0:
            return
        else:
            cur = self.head
            new_node = ListNode(val)
            for _ in range(index):
                cur = cur.next
            new_node.next = cur.next
            cur.next = new_node
            self.size += 1

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