19.1.29 [LeetCode 21] Merge Two Sorted Lists

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

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode*head=new ListNode(0);
        ListNode*ans = head;
        while (l1&&l2) {
            if (l1->val < l2->val) {
                head->next = l1;
                l1 = l1->next;
            }
            else {
                head->next = l2;
                l2 = l2->next;
            }
            head = head->next;
        }
        if (l1)head->next = l1;
        else if (l2)head->next = l2;
        return ans->next;
    }
};