Javascript Program For Making Middle Node Head In A Linked List

// Javascript program to make middle node 
// as head of Linked list

// Link list node 
class Node {
    constructor(val) {
        this.data = val;
        this.next = null;
    }
}

let head;

// Function to get the middle and set at 
// beginning of the linked list
function setMiddleHead() {
    if (head == null)
        return;

    // To traverse list nodes one
    // by one
    one_node = head;

    // To traverse list nodes by
    // skipping one.
    two_node = head;

    // To keep track of previous of middle
    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.
function push(new_data) {
    // Allocate 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
function printList(ptr) {
    while (ptr != null) {
        console.log(ptr.data);
        ptr = ptr.next;
    }
}

// Driver function 

// Create a list of 5 nodes
head = null;
let i;
for (i = 5; i > 0; i--)
    push(i);

console.log(" list before: ");
printList(head);

setMiddleHead();

console.log(" list After:  ");
printList(head);
// This code is contributed by aashish1995