leetcode：Merge Two Sorted Lists （链接两个有序链表）【面试算法题】

题目：

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.

题意链接两个有序链表。

没啥难点，注意头指针的建立和空指针。

/**
 * 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 *root,*p;
        root=new ListNode(-1);
        p=root;
        while(1)
        {
            if(l1==NULL){p->next=l2;break;}
            if(l2==NULL){p->next=l1;break;}
            if(l1->val<l2->val)
            {
                p->next=l1;
                l1=l1->next;
            }
            else
            {
                p->next=l2;
                l2=l2->next;
            }
            p=p->next;
        }
        ListNode *temp=root->next;
        delete(root);
        return temp;
    }
};
//http://blog.csdn.net/havenoidea