水題

class Solution {
public:
	ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
		if (l1 == NULL&&l2 == NULL)return l1;
		ListNode *firstNode = new ListNode(0);
		ListNode *p = new ListNode(0);
		firstNode->next = p;
		while (l1 && l2) {
			if (l1->val < l2->val)
 
 {
				p->next = new ListNode(l1->val);
				p = p->next;
				l1 = l1->next;
			}
			else {
				p->next = new ListNode(l2->val);
				p = p->next;
				l2 = l2->next;
			}
		}
		if (l1)p->next = l1;
		else p->next = l2;
		firstNode = firstNode->next->next;
		return firstNode;
 

	}
};