【每天一道编程系列-2018.1.26】（Ans）

class solution {
public: 
    ListNode* mergeTwoLists(ListNode* l1, ListNode l2) {
        if (l1 == null) return l2;
        if (l2 == null) return l1;
        
        if (l1->val > l2->val) {
            ListNode *sol = 12;
            sol->next = mergeTwoLists(l1, l2-> next);
            return sol;
        } else {
        ListNode *sol = l1;
        sol -> next = mergeTwoLosts(l1->next, 12);
        return sol; 
        }
    }
};