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.

代码如下：

class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if(l1 == NULL)
return l2;
if(l2 == NULL)
return l1;

ListNode *dummy = new ListNode(0);
ListNode *MergedList = dummy;

while(l1 && l2){
if(l1->val < l2->val){
dummy->next = l1;
l1 = l1->next;
}else{
dummy->next = l2;
l2 = l2->next;
}
dummy = dummy->next;

}

if(l1){
dummy->next = l1;
}

if(l2){
dummy->next = l2;
}

return MergedList->next;

}
};