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 lis

相对还是简单的，直接合并。

/** * 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 || !l2) return l1? l1:l2;        ListNode* head = new ListNode(0);        ListNode* node = head;        while (l1 && l2){            if (l1->val < l2->val){                node->next = l1;                l1 = l1->next;            }            else {                node->next = l2;                l2 = l2->next;            }            node = node->next;        }        node->next = l1?l1:l2;        return head->next;    }};