创建一个新链表
两个链表比较,小于等于取下来尾插
循环结束条件为任意一个链表为空
最后将之剩下的链表直接尾插
struct ListNode* mergeTwoLists(struct ListNode* list1, struct ListNode* list2){
if(list1 == NULL)
return list2;
if(list2 == NULL)
return list1;
struct ListNode *head = NULL,*tail = NULL;
while(list1 && list2)
{
if(list1->val <= list2->val)
{
if(head == NULL)
{
head = tail = list1;
}
else
{
tail->next = list1;
tail = tail->next;
}
list1 = list1->next;
}
else
{
if(head == NULL)
{
head = tail = list2;
}
else
{
tail->next = list2;
tail = tail->next;
}
list2 = list2->next;
}
}
if(list1)
tail->next = list1;
if(list2)
tail->next = list2;
return head;
}