100DaysOfCode/21.MergeTwoSortedList.cpp at master · ritvikroy/100DaysOfCode · GitHub

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/**
 * 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) {
        ListNode* dummy = new ListNode();
        ListNode* head = dummy;

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

        if(l1 != NULL)
            dummy->next = l1;
        else dummy->next = l2;

        return head->next;
    }
};