LeetCode 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.

一，算法分析

类似两个数组的合并，注意OJ给的链表默认是不带头结点的；另外两个数相等的时候可以归到大于或小于中进行处理

二、C语言实现

/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
struct ListNode *next1,*next2,*temp,*pre,*head;
next1=l1;
next2=l2;//这些链表默认都是不太头节点的，也就是head就是指向第一个有信息的值
head->next=next1;
pre=head;
while(next1!=NULL && next2!=NULL){
if(next1->val < next2->val){
pre=next1;
next1=next1->next;
}else{
temp=next2->next;//暂时保存
next2->next=next1;
pre->next=next2;
next2=temp;
pre=pre->next;
}
}
if(next1==NULL && next2!=NULL){
pre->next=next2;
}
return head->next;
}