LeetCode 21. Merge Two Sorted Lists

将两个有序链表合称为一个有序链表。

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode l3(INT_MIN);
        ListNode* tail = &l3;
        while (l1 && l2) {
            if (l1->val < l2->val) {
                tail->next = l1;
                l1 = l1->next;
            }else{
                tail->next = l2;
                l2 = l2->next;
            }
            tail = tail->next;
        }
        tail->next = l1 ? l1 : l2;
        return l3.next;
    }
};