서로 인접하는 홀수번째와 짝수번째의 노드의 위치를 서로 자리 이동 시키는 문제
/**
* 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) {
const preHead = new ListNode(0,head)
let rear = preHead
while(rear.next?.next) {
const third = rear.next.next.next
const second = rear.next.next
const first = rear.next
first.next = third
second.next = first
rear.next = second
rear = rear.next.next
}
return preHead.next
};