合并两个有序链表

// 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) {
        ListNode *dummyHead = new ListNode(0);
        ListNode *cur = dummyHead;
        while(l1 != NULL && l2 != NULL){
            if (l1->val < l2->val){
                cur->next = l1;
                cur = cur->next;
                l1 = l1->next;
            }
            else{
                cur->next = l2;
                cur = cur->next;
                l2 = l2->next;
            }
        }
        if (l1 == NULL){
            cur->next = l2;
        }
        if (l2 == NULL){
            cur->next = l1;
        }

        return dummyHead->next;
    }
};