Java Program For Making Middle Node Head In A Linked List

// Java program to make middle node 
// as head of Linked list
public class GFG 
{     
    // Link list node 
    static class Node 
    {
        int data;
        Node next;
        Node(int data)
        {
            this.data = data;
            next = null;
        }
    }
    
    static Node head;
    
    /* Function to get the middle and 
       set at beginning of the linked list*/
    static void setMiddleHead()
    {
        if (head == null)
            return;
     
        // To traverse list nodes one 
        // by one
        Node one_node = head;
     
        // To traverse list nodes by 
        // skipping one.
        Node two_node = head;
     
        // To keep track of previous of middle
        Node prev = null;
        while (two_node != null && 
               two_node.next != null) 
        {     
            // For previous node of middle node 
            prev = one_node;
     
            // Move one node each time
            two_node = two_node.next.next;
     
            // Move two node each time
            one_node = one_node.next;
        }
     
        // Set middle node at head 
        prev.next = prev.next.next;
        one_node.next = head;
        head = one_node;
    }
     
    // To insert a node at the beginning 
    // of linked list.
    static void push(int new_data)
    {
        // Allocate node 
        Node new_node = new Node(new_data);
     
        // Link the old list of the new node 
        new_node.next = head;
     
        // Move the head to point to the 
        // new node 
        head = new_node;
    }
     
    // A  function to print a given linked list
    static void printList(Node ptr)
    {
        while (ptr != null) 
        {
            System.out.print(ptr.data + " ");
            ptr = ptr.next;
        }
        System.out.println();
    }
     
    // Driver function
    public static void main(String args[])
    {
        // Create a list of 5 nodes
        head = null;
        int i;
        for (i = 5; i > 0; i--)
            push(i);
        
        System.out.print(" list before: ");
        printList(head);
     
        setMiddleHead();
     
        System.out.print(" list After:  ");
        printList(head);
    
    }
}
// This code is contributed by Sumit Ghosh