SDESheet/mergeTwoListsCpp at main · Karthilearns/SDESheet · GitHub

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class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        // iterative
        ListNode* res = new ListNode();
        ListNode *temp = res;

        while(l1 != NULL && l2!=NULL) {
            if(l1->val < l2->val) {
                res->next = l1;
                res = res -> next;
                l1 = l1->next;
            }
            else {
                res->next = l2;
                res = res->next;
                l2 = l2->next;
            }
        }
        while(l1 != NULL) {
            res->next = l1;
            res = res -> next;
            l1 = l1->next;
        }
        while(l2 != NULL) {
            res->next = l2;
            res = res -> next;
            l2 = l2->next;
        }

        return temp->next;
    }
};