Leetcode日记（2）---Add two numbers

#include<stddef.h>

using namespace std;

struct ListNode{
int val;
ListNode *next;
ListNode(int x):val(x), next(NULL){}
};

class Solution{
public:
ListNode *addTwoNumbers(ListNode  *l1 , ListNode  *l2){
int carry = 0;
ListNode* tail = new ListNode(0);  // kai shi lian biao shi shu zi wei 0 de lian biao
ListNode* ptr = tail;

while(l1 != NULL || l2 != NULL){
int val1=0;
if(l1 != NULL){
val1 = l1->val;
l1 = l1 ->next;
}

int val2 = 0;
if(l2 != NULL){
val2 = l2->val;
l2 = l2 ->next;
}

int tmp = val1 + val2 +carry;
ptr->next = new ListNode(tmp % 10) ;  // zhi liu xia ge wei shu zi
carry = tmp /10 ;
ptr = ptr ->next;
}

if (carry == 1){
ptr->next = new ListNode(1);
}

return tail->next;

}
};

int main(){
return 0;
}