swap-nodes-in-pairs.js

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */

var swapPairs = function(head) {

    // Initialise a dummy list containing the provided one
    
    let dummyList = new ListNode(null, head);

    // Create a copy of the dummy list which we can traverse with
    
    let current = dummyList;

    // While there are 2 additional elements remaining
   
    while (current.next && current.next.next) {
       
        // Obtain the nodes to be swapped
        
        const first = current.next;
        const second = current.next.next;

        // Swap the nodes
        
        first.next = second.next;
        second.next = first;
        current.next = second;

        // Move forward by 2 elements
        
        current = current.next.next;
    }

    // Return the swapped LinkedList, removing the dummy head
    
    return dummyList.next;
    
};