Leecode24_swapPairs

代码：

// 两两交换链表的节点
class Solution {
public:
    ListNode* Leecode24_swapPairs(ListNode* head) {
    if (head == nullptr || head->next == nullptr)
		return head;
	ListNode *firstNode = head;
	ListNode *secondNode = head->next;
	firstNode->next = Leecode24_swapPairs(secondNode->next);
	secondNode->next = firstNode;
	return secondNode; 
    }
};