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题意：
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： 两个有序链表归并，没啥说的，唯一要说的，ptr指针不要忘记后移
/**
* 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) {
if(l1 == NULL) return l2;
if(l2 == NULL) return l1;
ListNode *root = new ListNode(0);
ListNode * ptr = root;
while(l1!=NULL && l2!=NULL)
{
if(l1->val <= l2->val)
{
ptr->next = l1;
l1 = l1->next;
}
else
{
ptr->next = l2;
l2 = l2->next;
}
ptr = ptr->next;
}
while(l1)
{
ptr->next = l1;
l1 = l1->next;
ptr = ptr->next;
}
while(l2)
{
ptr->next = l2;
l2 = l2->next;
ptr = ptr->next;
}
ptr = root->next;
delete root;
return ptr;
}
};
LeetCode 21. Merge Two Sorted Lists
原文：http://www.cnblogs.com/gufeiyang/p/5203456.html