/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if(!l1){
            return l2;
        }
        if(!l2){
            return l1;
        }
        ListNode* s;
        if(l1->val <= l2->val){
            s=l1;
            l1=l1->next;
        }
        else{
            s=l2;
            l2=l2->next;
        }
        ListNode* l3=s;
        while(l1 && l2){
            if(l1->val <= l2->val){
              s->next=l1;
              s=l1;
              l1=s->next;
        }
            else{
                s->next = l2;
                s = l2;
                l2 = s->next;
            }
        }
        if(!l1){
            s->next=l2;
        }
        else{
            s->next=l1;
        }
        return l3;
    }
        
    
};
