Leetcode 21. Merge Two Sorted Lists

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

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if(l1==NULL) return l2;
        if(l2==NULL) return l1;
        if(l1->val>l2->val) return mergeTwoLists(l2,l1);
        ListNode *ans=l1,*p=l1;
        l1=l1->next;
        while(l1 && l2){
            if(l1->val < l2->val){
                ans->next=l1;
                ans=ans->next;
                l1=l1->next;
            }else{
                ans->next=l2;
                ans=ans->next;
                l2=l2->next;
            }
        }
        if(l1) ans->next=l1;
        else ans->next=l2;
        return p;
    }
};

python版本

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        head=ListNode(1)
        p=head
        while l1!=None and l2!=None:
            if l1.val>l2.val:
                p.next=l2
                l2=l2.next
            else:
                p.next=l1
                l1=l1.next
            p=p.next
        if l1==None:
            p.next=l2
        else:
            p.next=l1
        return head.next