[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.

class Solution {public:    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2)     {        if(l1 == NULL)           return l2;        if(l2 == NULL)           return l1;                ListNode* MergeHead = NULL;        if(l1->val <= l2->val)            {                MergeHead = l1;                MergeHead->next = mergeTwoLists(l1->next,l2);            }        else            {                MergeHead = l2;                MergeHead->next = mergeTwoLists(l1,l2->next);            }        return MergeHead;    }};