merge-two-sorted-lists.cpp

/**
 * 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 ||l1->val > l2->val){
            return mergeTwoLists(l2, l1);
        }
        l1->next = mergeTwoLists(l1->next, l2);
        return l1;
    }
};