LeetCode 21 Merge Two Sorted Lists

题目

/**
 * 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* ans = new ListNode(0);
        ListNode* res = ans;

       
        while(l1!=NULL||l2!=NULL)
        {
            if(l1==NULL)
            {
                res->next = new ListNode(l2->val);
                l2=l2->next;
                res=res->next;
                continue;
            }
            if(l2==NULL)
            {
                
                res->next = new ListNode(l1->val);;
                l1=l1->next;
                res=res->next;
                continue;
            }
            
            if(l1->val<=l2->val)
            {
                     res->next = new ListNode(l1->val);
                l1=l1->next;
            }
            else
            {
                      res->next = new ListNode(l2->val);
               
                l2=l2->next;
            }
            
            res=res->next;
        }
        
        return ans->next;
    }
};