Untitled

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        if(!list1 && !list2)
            return nullptr;
        else if(list2 && !list1)
            return list2;
        else if (list1 && !list2)
            return list1;


        ListNode* result = nullptr, *cur = nullptr;    
        if(list1->val < list2->val)
        {
            result = cur = list1;
            list1 = list1->next;
        }
        else
        {
            result = cur = list2;
            list2 = list2->next;
        }

        while(list1 && list2)
        {
            if(list1->val < list2->val)
            {
                auto temp = list1->next;
                cur->next = list1;
                cur = cur->next;
                list1 = temp;
            }
            else
            {
                auto temp = list2->next;
                cur->next = list2;
                cur = cur->next;
                list2 = temp;
            }
        }

        if(list1)
            cur->next = list1;
        if(list2)
            cur->next = list2;

        return result;
    }
};