design_linked_list.cpp

//program for design linked list
//problem link: https://leetcode.com/problems/design-linked-list/


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

};

class MyLinkedList {
public:
    Node * head = NULL;
    Node * tail = NULL;
    int size = 0;

    MyLinkedList() {
        
    }
    
    int get(int index) {
        if(index >= size || index < 0) return -1;
        else if(head == NULL) return -1;
        else if(index == 0 ) return head -> val;
        else if(index == size -1) return tail -> val;
        Node * tmp = head;
        for(int i = 1; i < index; i++)
        {
            tmp = tmp -> next;
        }
        return tmp -> next ->  val;
    }
    
    void addAtHead(int val) {
        size ++;
        Node * newNode = new Node(val);
        if(head == NULL)
        {
            head = newNode; tail = newNode; 
            return;
        }
        newNode -> next = head;
        head -> prev = newNode;
        head = newNode;
    }
    
    void addAtTail(int val) {
        size ++;  
        Node * newNode = new Node(val);
        if(head == NULL)
        {
            head = newNode;
            tail = newNode;
            return;
        }
        tail -> next = newNode;
        newNode -> prev = tail;
        tail = newNode;
    }
    
    void addAtIndex(int index, int val) {
        if(index > size) return;
        else if(index < 0) return;
        else if(index == size)addAtTail(val);
        else if(index == 0) addAtHead(val);
        else{
            Node * tmp = head;
            Node * newNode = new Node(val);
            for(int i = 1; i<index ; i++)
            {
                tmp = tmp -> next;
            }
            tmp -> next -> prev = newNode;
            newNode -> next = tmp -> next;
            newNode ->  prev = tmp;
            tmp -> next = newNode;
            size ++;
        }
    }
    
    void deleteAtIndex(int index) {
        if(index < 0 || index >= size) return;
        else if(head == NULL) return;
        else if(index == 0)
        {
            Node * delNode = head;
            head = head -> next;
            if(head != NULL) head -> prev = NULL;
            if(head == NULL) tail = NULL;
            delete delNode;
            size --;
        }
        else if(index == size -1)
        {
            Node * delNode = tail;
            tail = tail -> prev;
            tail -> next = NULL;
            if(tail == NULL) head = NULL;
            size --;
        }
        else
        {
            Node * tmp = head;
            for(int i = 1; i < index; i++)
            {
                tmp  = tmp  -> next;
            }
            Node * delNode = tmp -> next;
            if(tmp  -> next -> next != NULL) tmp -> next -> next ->  prev = tmp;
            tmp -> next = tmp -> next -> next;
            delete delNode;
            size --;
        }
    }
};