Array to linked list

Use Node Represents a linked list node

public class Node {
    public int val;
    public Node next=null;

    public Node(int val) {
        this.val = val;
    }

    @Override
    public String toString() {
        return "["+val+"]";
    }
}

Main method

public class mmain {
    public static void main(String[] args) {
//         Create array 
        int[] array={1,2,3,4,5};
//        Node head=arrayTolinkedList(array);
        Node head=arrayTolinkedList2(array);
        print(head);
    }

Method 1 （ Without puppet node ）

   public static Node arrayTolinkedList(int[] array){
        // Traversal array , Insert the elements in sequence 
        // If every tail insertion , You need to know the end node of the current linked list 
        // You can directly use a reference to remember the tail node 

        //head It is the reference of the header node , In the initial case , The list is empty 
        Node head=null;
        //tail It's also empty 
        Node tail=null;
        for (int x:array){
            Node node=new Node(x);
            // hold Node Perform tail insertion 
            // You need to determine whether the current linked list is empty 
            if (head==null){
                head=node;
                tail=node;
            }else{
                // When the linked list is not empty , Then insert new , Don't worry head 了 , Direct manipulation tail That's it 
                tail.next=node;
                // Once the insertion is complete , The new node becomes tail, You need to update tail The direction of 
                tail=tail.next;
            }
        }
        return head;
    }

Method 2 （ With puppet node ）

Do it in a simpler way , If we create a puppet node , Subsequent tail insertion operation , There is no need to discuss it in two cases .

public static Node arrayTolinkedList2(int[] array) {
        Node head=new Node(0);// Puppet node 
        // Also create a tail Reference to save the tail of the linked list 
        Node tail=head;

        for (int x:array){
            Node node=new Node(x);
            tail.next=node;
            tail=tail.next;
        }
        // The requirement of the code is that the returned result is a linked list without dummy nodes 
        // If you return head,head It points to the puppet node , Unqualified .
        return head.next;
    }

Print function

        public static void print(Node head) {
            for (Node cur=head;cur!=null;cur=cur.next){
                System.out.println(cur.val);
            }
        }

//      public static void print(Node node) {
//        while (node != null) {
//            System.out.println(node.val);
//            node = node.next;
//        }
       }