LeetCode24. 两两交换链表中的节点

 

    public ListNode swapPairs(ListNode head) {
        if(head == null || head.next == null)return head;
        ListNode one = head;
        ListNode two = one.next;
        ListNode tmp = two.next;
        two.next = one;
        one.next = swapPairs(tmp);
        return two;
    }