【21】Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

简单的链表题，加一个头节点方便编码

ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) { ListNode* head=new ListNode(0); ListNode* p=head; while(l1 || l2){ if((l1 && l2 && (l1->val < l2->val)) || !l2){ p->next=l1; l1=l1->next; p=p->next; } else{ p->next=l2; l2=l2->next; p=p->next; } } return head->next; }