algorithms/21.cpp at main · snehashish090/algorithms · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
/**
 * 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* list1, ListNode* list2) {
        if (list1 == nullptr && list2 == nullptr)
            return nullptr;
        else if (list1 == nullptr && list2 != nullptr)
            return list2;
        else if (list2 == nullptr && list1 != nullptr)
            return list1;

        ListNode* nextNode1 = list1->next;
        ListNode* nextNode2 = list2->next;

        if (list1->val <= list2->val)
        {
            if (nextNode1 && nextNode1->val < list2->val)
                list1->next = mergeTwoLists(nextNode1, list2);
            else{
                list1->next = list2;
                list2 ->next = mergeTwoLists(nextNode1, nextNode2);
            }
            return list1;
        }
        else
        {
            if (nextNode2 && nextNode2->val < list1->val)
                list2->next = mergeTwoLists(list1, nextNode2);
            else{
                list2->next = list1;
                list1 ->next = mergeTwoLists(nextNode1, nextNode2);
            }
            return list2;
        }
    }
};