Leetcode - 707 design linked list (Design)

Single chain list

Be careful Add node for the first time perhaps addAtIndex（ The added node is at the end ）deleteAtIndex（ Deleted the end node ） May cause the tail pointer to change To judge and update the tail pointer

class MyLinkedList {
    
    class Node{
    
        int val;// The value of the node 
        Node next;// Node next The pointer 
        public Node(int val){
    
            this.val = val;
        }
    }
    private Node head;// Head node 
    private Node tail;// Tail node 
    public MyLinkedList() {
    
         head = new Node(0);// Set up the head node   The head node does not store values   The first value is stored in the header node next in 
         tail = head;// The tail pointer points to the head node 
    }
    
    public int get(int index) {
    
        // i  and  node To correspond  i = 0  Is precisely head.next
        // The head node does not store values   The first value is stored in the header node next in  
       int i = 0;
       Node node = head.next;
       // Traverse to find index Corresponding node 
       while(i < index && node != null){
    
           node = node.next;
           i++;
       }
       // There is... In the linked list index Corresponding node 
       if(node != null)// Return its value 
          return node.val;
       else
          return -1;
    }
    
    public void addAtHead(int val) {
    
        // The new node 
         Node node = new Node(val);
        // Insert this node into the head node and the head node .next Between 
         node.next = head.next;
         head.next = node; 
         // If there is only one node in the current linked list 
         // Point the tail pointer to the node 
         if(node.next == null)
            tail = node;
    }
    
    public void addAtTail(int val) {
    
        // The new node 
        Node node = new Node(val);
        // Add it after the tail node 
        tail.next = node;
        // At this point, this node becomes the end node   Point the tail pointer to it 
        tail = node;
    }
    
    public void addAtIndex(int index, int val) {
    
        // Search for the first index-1 Nodes 
         int i = -1;
         Node node = head;
         while(i < index-1 && node != null){
    
             i++;
             node = node.next;
         }
         // If there is a second index-1 Nodes 
         if(node != null)
         {
    
             // The new node 
             Node addNode = new Node(val);
             addNode.next = node.next;
             node.next = addNode;
             // Note that updates may be added to the end tail
             if(addNode.next == null)
                 tail = addNode;
         }
         
    }
    
    public void deleteAtIndex(int index) {
    
        // Search for the first index-1 Nodes 
         int i = -1;
         Node node = head;
         while(i < index-1 && node != null){
    
             i++;
             node = node.next;
         }
         // There is No index-1 Nodes 
         // And then there is the third index Nodes 
         if(node != null && node.next!=null)
         {
    
             // Delete the first index Nodes 
            node.next = node.next.next;
            // Maybe the last node was deleted 
             if(node.next == null){
    
                tail = node;
            }
         }
    }
}

/** * Your MyLinkedList object will be instantiated and called as such: * MyLinkedList obj = new MyLinkedList(); * int param_1 = obj.get(index); * obj.addAtHead(val); * obj.addAtTail(val); * obj.addAtIndex(index,val); * obj.deleteAtIndex(index); */