Problem Statement:
Design your implementation of the linked list. You can choose to use a singly or doubly linked list.
A node in a singly linked list should have two attributes:Â val
 and next
. val
 is the value of the current node, and next
 is a pointer/reference to the next node.
If you want to use the doubly linked list, you will need one more attribute prev
 to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.
Implement the MyLinkedList
 class:
MyLinkedList()
 Initializes theÂMyLinkedList
 object.int get(int index)
 Get the value of theÂindexth
 node in the linked list. If the index is invalid, returnÂ-1
.void addAtHead(int val)
 Add a node of valueÂval
 before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.void addAtTail(int val)
 Append a node of valueÂval
 as the last element of the linked list.void addAtIndex(int index, int val)
 Add a node of valueÂval
 before theÂindexth
 node in the linked list. IfÂindex
 equals the length of the linked list, the node will be appended to the end of the linked list. IfÂindex
 is greater than the length, the node will not be inserted.void deleteAtIndex(int index)
 Delete theÂindexth
 node in the linked list, if the index is valid.
Example 1:
Input [“MyLinkedList”, “addAtHead”, “addAtTail”, “addAtIndex”, “get”, “deleteAtIndex”, “get”] [[], [1], [3], [1, 2], [1], [1], [1]] Output [null, null, null, null, 2, null, 3]
Explanation MyLinkedList myLinkedList = new MyLinkedList(); myLinkedList.addAtHead(1); myLinkedList.addAtTail(3); myLinkedList.addAtIndex(1, 2); // linked list becomes 1→2→3 myLinkedList.get(1); // return 2 myLinkedList.deleteAtIndex(1); // now the linked list is 1→3 myLinkedList.get(1); // return 3
Constraints:
0 <= index, val <= 1000
- Please do not use the built-in LinkedList library.
- At mostÂ
2000
 calls will be made toÂget
,ÂaddAtHead
,ÂaddAtTail
,ÂaddAtIndex
andÂdeleteAtIndex
.