21. Merge Two Sorted Lists*

21. Merge Two Sorted Lists*

https://leetcode.com/problems/merge-two-sorted-lists/

Title Description

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

C ++ implementation 1

The subject is not difficult, in addition, the list of questions is generally set up a virtual node dummywill save a lot of trouble.

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if (!l1 && !l2) return nullptr;
        ListNode *dummy = new ListNode(0);
        auto p = dummy;
        while (l1 && l2) {
            if (l1->val < l2->val) {
                p->next = l1;
                l1 = l1->next;
            } else {
                p->next = l2;
                l2 = l2->next;
            }
            p = p->next;
        }
        p->next = l1 ? l1 : l2;
        return dummy->next;
    }
};