Merge Two Sorted Lists - LeetCode

解题思路：

新建一个linklist， 将两个序列中最小值分别赋值给新序列，当一个序列为空时将另一个序列接到新建序列上。

class Solution {public:    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {        if(l1 == NULL) return l2;        if(l2 == NULL) return l1;                ListNode *head = new ListNode(-1);          ListNode *res = head;                while(l1 != NULL && l2 != NULL)        {            if(l1->val < l2->val)            {                res->next = l1;                res = res->next;                l1 = l1->next;            }            else if(l1-> val >= l2-> val)            {                res->next = l2;                res = res->next;                l2 = l2->next;            }        }                if(l1 == NULL)        {            res->next = l2;        }        else if(l2 == NULL)        {            res->next = l1;        }        res = head->next;        delete head;        return res;    }};