707_design_linked_list

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

class MyLinkedList:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.head = None
        self.size = 0
        

    def get(self, index):
        """
        Get the value of the index-th node in the linked list. If the index is invalid, return -1.
        :type index: int
        :rtype: int
        """
        if index < 0 or index >= self.size:
            return -1
        if self.head == None:
            return -1
        curr = self.head
        for i in range(index):
            curr = curr.next
        return curr.val
    
    

    def addAtHead(self, val):
        """
        Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
        :type val: int
        :rtype: void
        """
        node = Node(val)
        node.next = self.head
        self.head = node
        self.size += 1
        
        

    def addAtTail(self, val):
        """
        Append a node of value val to the last element of the linked list.
        :type val: int
        :rtype: void
        """
        node = Node(val)
        curr = self.head
        if curr is None:
            self.head = node
        else:
            while curr.next is not None:
                curr = curr.next
            curr.next = node
        self.size += 1
        

    def addAtIndex(self, index, val):
        """
        Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted.
        :type index: int
        :type val: int
        :rtype: void
        """
        if index < 0 or index > self.size:
            return
        
        if index == 0:
            self.addAtHead(val)
        else:
            curr = self.head
            for i in range(index - 1):
                curr = curr.next
            node = Node(val)
            node.next = curr.next
            curr.next = node
            
            self.size += 1

    def deleteAtIndex(self, index):
        """
        Delete the index-th node in the linked list, if the index is valid.
        :type index: int
        :rtype: void
        """
        if index < 0 or index >= self.size:
            return
        curr = self.head
        if index == 0:
            self.head = curr.next
        else:
            for i in range(index-1):
                curr = curr.next
            curr.next = curr.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)