leetcode-cpp/0021.cpp at main · s4nj1th/leetcode-cpp · GitHub

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

        if (list2 == nullptr)
            return list1;

        if (list1->val <= list2->val) {
            list1->next = mergeTwoLists(list1->next, list2);
            return list1;
        }

        list2->next = mergeTwoLists(list1, list2->next);
        return list2;
    }
};

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        ListNode dummy(0);
        ListNode* tail = &dummy;

        while (list1 != nullptr && list2 != nullptr) {
            if (list1->val <= list2->val) {
                tail->next = list1;
                list1 = list1->next;
            } else {
                tail->next = list2;
                list2 = list2->next;
            }

            tail = tail->next;
        }

        if (list1 != nullptr)
            tail->next = list1;

        if (list2 != nullptr)
            tail->next = list2;

        return dummy.next;
    }
};