leetcode 24. Swap Nodes in Pairs (medium)

class Solution
{
public:
	ListNode *swapPairs(ListNode *head)
	{
		if (head == nullptr || head->next == nullptr)
			return head;
		ListNode dummy(-1);
		dummy.next = head;
		ListNode *pre = &dummy;
		ListNode *cur = pre->next;
		ListNode *next = cur->next;
		while ((cur = pre->next) && (next = cur->next))
		{
			cur->next = next->next;
			next->next = cur;
			pre->next = next;
			pre = cur;
		}
		return dummy.next;
	}
};