双链表：在前面添加一个节点。来自geeksforgeeks（java代码）

Question

//类用于双链表公共类DLL{节点head；//列表head

/* Doubly Linked list Node*/
class Node { 
    int data; 
    Node prev; 
    Node next; 

    // Constructor to create a new node 
    // next and prev is by default initialized as null 
    Node(int d) { data = d; } 
} 
// Adding a node at the front of the list 
public void push(int new_data) 
{ 
/* 1. allocate node  
* 2. put in the data */
    Node new_Node = new Node(new_data); 

/* 3. Make next of new node as head and previous as NULL */
new_Node.next = head; 
new_Node.prev = null; 

/* 4. change prev of head node to new node */
    if (head != null) 
        head.prev = new_Node; 

/* 5. move the head to point to the new node */
    head = new_Node; 
} 

}

Answer 1

需要第4步将旧磁头的prev连接到新磁头。

这是步骤3之后的情况：

然后，在第4步之后，将旧头部（为null）的prev设置为指向新头部：