/**
 * 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) {
	// base case
    if (!head || !head.next) return head;
    
    const newHead = head.next;
    let curHead = head;
    
    while (curHead && curHead.next) {

        let temp = curHead;
        curHead = curHead.next;
        temp.next = curHead.next;
        curHead.next = temp;
        curHead = temp.next;
        // if another pair point to next one
        if (curHead && curHead.next) {
            temp.next = curHead.next;
        }
    }
    
    return newHead;
};