# Design Linked List Problem

## Description

LeetCode Problem 707.

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:

• 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:

``````1
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Input
[[], [1], [3], [1, 2], [1], [1], [1]]
Output
[null, null, null, null, 2, null, 3]
Explanation
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.

## Sample C++ Code

``````1
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class Node {
public:
int val;
Node* next;
Node(int val) {
this->val = val;
next = NULL;
}
};

public:
int size = 0;
Node* head = new Node(0);

int get(int index) {
if (index >= size) return -1;
Node* temp = head->next;
for (int i = 0; i < index; i++)
temp = temp->next;
return temp->val;
}

Node* temp = head->next;
head->next = new Node(val);
size++;
}

void addAtTail(int val) {
Node* temp = head;
while(temp->next != NULL)
temp = temp->next;
temp->next = new Node(val);
size++;
}

void addAtIndex(int index, int val) {
if (index > size)
return;
Node* temp = head;
for (int i = 0; i < index; i++)
temp = temp->next;
Node* temp1 = temp->next;
temp->next = new Node(val);
temp->next->next = temp1;
size++;
}

void deleteAtIndex(int index) {
if (index >= size)
return;
Node* temp = head;
for (int i = 0; i < index; i++)
temp = temp->next;
Node* temp1 = temp->next;
temp->next = temp1->next;
temp1->next = NULL;
size--;
delete temp1;
}
};
/**
* Your MyLinkedList object will be instantiated and called as such:
* int param_1 = obj->get(index);
* obj->deleteAtIndex(index);
*/
``````