w3.q14

static int __=[](){cin.tie(0);std::ios::sync_with_stdio(false);return 0;}();

struct node{
    int data;
    node* next;
    node(int d){
        data = d;
        next = NULL;
    }
};

class MyLinkedList {
public:
    /** Initialize your data structure here. */
    node* head;
    node* tail;
    int size;
    MyLinkedList() {
        head = NULL;
        tail = NULL;
        size = 0;
    }
    
    /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
    int get(int index) {
        
        if(index>=size || index < 0 || size == 0){
            return -1;
        }
        
        node* itr = head;
        
        for(int i=0; i<index; i++){
            itr = itr->next;
        }
        return itr->data;
    }
    
    /** 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 addAtHead(int val) {
        node* newNode = new node(val);
        
        //If head is not initialized
        if(head == NULL){
            head = newNode;
            tail = newNode;
            size = 1;
            return;
        }
        
        //Adding newNode to head
        newNode->next = head;
        head = newNode;
        size+=1;
        return;
    }
    
    /** Append a node of value val to the last element of the linked list. */
    void addAtTail(int val) {
       node* newNode = new node(val);
        
        //If head is not initialized
        if(head == NULL){
            head = newNode;
            tail = newNode;
            size = 1;
            return;
        }
        
        //Adding newNode at tail
        tail->next = newNode;
        tail = newNode;
        size+=1;
        return; 
    }
    
    /** 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. */
    void addAtIndex(int index, int val) {
        //If invalid index
        if(index > size){
            return;
        }
        //Add at the end
        else if(index == size){
            addAtTail(val);
        }
        //Add at the starting
        else if(index == 0){
            addAtHead(val);
        }
        //Add somewhere in middle
        else{
            node* newNode = new node(val);
            
            node* itr = head;
            
            //Mode itr to one index before the place where new node needs to be inserted
            for(int i=0; i<index-1; i++){
                itr = itr->next;
            }
            newNode->next = itr->next;
            itr->next = newNode;
            size+=1;
        }
    }
    
    /** Delete the index-th node in the linked list, if the index is valid. */
    void deleteAtIndex(int index) {
        
        //If Invalid Index
        if(index >= size){
            return;
        }
        //Deleted from head
        else if(index == 0){
            //If only one element present
            if(size == 1){
                head = tail = NULL;
                size = 0;
            }
            else{
                //Simply move head to next
                head = head->next;
                size-=1;
            }
        }
        else{
            node *itr = head;
            
            //Move itr to one node before the node to be deleted
            for(int i=0; i<index-1; i++){
                itr = itr->next;
            }
            
            itr->next = itr->next->next;
            
            if(itr->next == NULL){
                tail = itr;
            }
            size-=1;
        }
        
    }
};