请你手写代码，如何合并两个有序链表

参考回答：

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