707. Design Linked List

Description

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: 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 the MyLinkedList object.
int get(int index) Get the value of the index^th node in the linked list. If the index is invalid, return -1.
void addAtHead(int 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.
void addAtTail(int val) Append a node of value val as the last element of the linked list.
void addAtIndex(int index, int val) Add a node of value val before the index^th node in the linked list. If index equals the length of the linked list, the node will be appended to the end of the linked list. If index is greater than the length, the node will not be inserted.
void deleteAtIndex(int index) Delete the index^th 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 most 2000 calls will be made to get, addAtHead, addAtTail, addAtIndex and deleteAtIndex.

Solution

design-linked-list.py

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

class MyLinkedList:

    def __init__(self):
        self.head = None
        self.size = 0

    def get(self, index: int) -> int:
        if index < 0 or index >= self.size or not self.head: return -1

        curr = self.head
        for _ in range(index):
            curr = curr.next

        return curr.val

    def addAtHead(self, val: int) -> None:
        node = Node(val)
        node.next = self.head

        self.head = node
        self.size += 1

    def addAtTail(self, val: int) -> None:
        curr = self.head

        if not curr:
            self.head = Node(val)
        else:
            while curr.next:
                curr = curr.next
            curr.next = Node(val)

        self.size += 1

    def addAtIndex(self, index: int, val: int) -> None:
        if index == 0:
            self.addAtHead(val)
            return

        if index == self.size:
            self.addAtTail(val)
            return

        if not (0 <= index < self.size): return

        node = Node(val)
        curr = self.head

        for _ in range(index - 1):
            curr = curr.next

        nxt = curr.next
        curr.next = None
        node.next = nxt
        curr.next = node
        self.size += 1


    def deleteAtIndex(self, index: int) -> None:
        if index == 0:
            self.head = self.head.next
            self.size -= 1
            return

        if not (0 <= index < self.size): return

        curr = self.head

        for _ 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)