leetcode: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.

两个已经排序的链表，按照升序组合为一个链表

/**
 * 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 *ret = NULL;
    
    if (l1->val < l2->val)
    {
        ret = l1;
        ret->next = mergeTwoLists(l1->next, l2);
    }
    else
    {
        ret = l2;
        ret->next = mergeTwoLists(l1, l2->next);
    }
    
    return ret;
    }
};