LeetCode | 21. merge two ordered lists

The two ordered lists into a new sorted list and return. The new list is by all nodes in a given mosaic composed of two lists.

Example:

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

Solution: Merge method

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode *dummy = new ListNode(0);
        ListNode *cur = dummy;
        while(l1 && l2)
        {
            if(l1->val <l2->val)
            {
                cur->next = l1;
                l1 = l1->next;
            }
            else{
                cur->next = l2;
                l2 = l2->next;
            }
            cur = cur->next;
        }
        cur->next = l1 ? l1 :l2;//处理l1或者l2有剩余的情况
        return dummy->next;
    }
};

Solution: recursion

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if(!l1)return l2;
        if(!l2)return l1;
        
        if(l1->val < l2->val){
            l1->next = mergeTwoLists(l1->next,l2);
            return l1;
        }
        else{
            l2->next = mergeTwoLists(l1 , l2->next);
            return l2;
        }
    }
};