leetcode 24. 两两交换链表中的节点

又是递归

class Solution {
    public ListNode swapPairs(ListNode head) {
        if(head == null || head.next == null){
            return head;
        }
        
        ListNode temp = head.next;
        head.next = swapPairs(temp.next);
        temp.next = head;
        return temp;
    }
}