Java linkedlist insterting node 位于第一个位置

Question

我如何修改此代码，从将节点从第二个位置插入到第一个位置？

static void insertAtMid(int x)
{
if (head == null)
head = new Node(x);
else {
Node newNode = new Node(x);
Node ptr = head;
int len = 0;

while (ptr != null) {
len++;
ptr = ptr.next;
}

int count = (len >=1)? 1 : 0;
ptr = head;

while (count-- > 1)
ptr = ptr.next;

newNode.next = ptr.next;
ptr.next = newNode;
}
}
static void display()
{
Node temp = head;
while (temp != null)  
{
System.out.print(temp.data + " ");
temp = temp.next;
}
}
public static void main (String[] args)  
{  
head = null;
head = new Node(23);
head.next = new Node(45);
head.next.next = new Node(12);
head.next.next.next = new Node(67);
System.out.println("Linked list before "+
"insertion: ");
display();
int x = 55;
insertAtMid(x);
System.out.println("nLinked list after"+
" insertion: ");
display();
}  

Answer 1

要在链表的开头插入一个新节点，您所要做的就是创建一个新节点，然后将其next值设置为当前 head：

Node newHead = new Node(x);
newHead.next = head;

此时，新的头是newHead，它已入到列表的开头。

Answer 2

您可以使用临时变量并执行以下操作：

newNode = newNode() //the node you want to insert
tmp = head //assuming that head is accessible
head = newNode
newNode.next = tmp
head = newNode