Sorted LL

Merging

/**
 * 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:
    struct ListNode* header = NULL;
    struct ListNode* head = NULL;

    void newNode(int data) {
        if (header == NULL) {
            header = new ListNode(data);
            head = header;
        } else {
            struct ListNode* temp;
            temp = new ListNode(data);
            header->next = temp;
            header = header->next;
        }
    }
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {

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

        if (list1) {
            while (list1) {
                newNode(list1->val);
                list1 = list1->next;
            }
        } else {
            while (list2) {
                newNode(list2->val);
                list2 = list2->next;
            }
        }

        return head;
    }
};