将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。
示例:
输入:1->2->4, 1->3->4
输出:1->1->2->3->4->4
//4-16
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if(!l1&&l2)
return l2;
if(l1&&!l2)
return l1;
if(!l1&&!l2)
return l1;
//所给链表存在头节点
ListNode* res = l1;
ListNode* head = l1;
if(l1->val>=l2->val){//设定新链表的头节点
res = l2;
l2 = l2->next;
}
else{
res = l1;
l1 = l1->next;
}
head = res;
while(l1 && l2){
if(l1->val>=l2->val){
res->next = l2;
l2=l2->next;
}
else{
res->next = l1;
l1 = l1->next;
}
res = res->next;
}
if(l1)
res->next = l1;
else
res->next = l2;
return head;
}
};