[leetcode] 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.

思路：逐个遍历两条链，较小的拼接到新链后面

代码：

/**
* 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) {
ListNode *temp;
if(l1==NULL){
temp=l2;
return temp;
}
if(l2==NULL){
temp=l1;
return temp;
}
if(l1->val>l2->val){
temp=l2;
l2=l2->next;
}else{
temp=l1;
l1=l1->next;
}
ListNode *res;
res=temp;
while(l1!=NULL && l2!=NULL){
if(l1->val<l2->val){
temp->next=l1;
l1=l1->next;
}else{
temp->next=l2;
l2=l2->next;
}
temp=temp->next;
}
if(l1!=NULL) temp->next=l1;
if(l2!=NULL) temp->next=l2;
return res;
}
};