Leetcode43: 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.

用归并排序的思想。

/**
* 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* merge = new ListNode(0);
ListNode* head = merge;
while(l1&&l2)
{
if(l1->val < l2->val)
{
merge->next = l1;
l1 = l1->next;
merge = merge->next;
}
else
{
merge->next = l2;
l2 = l2->next;
merge = merge->next;
}
}

if(l1)
{
merge->next = l1;
}
if(l2)
{
merge->next = l2;
}

return head->next;
}
};