LeetCode Add Two Numbers

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     struct ListNode *next;
* };
*/
struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
struct ListNode* l3=l1,*p=l1;
int s=0,k=0;
while(l1&&l2)
{
k=l1->val+l2->val;
l1->val=(k+s)%10;
s=(k+s)/10;
p=l1;
l1=l1->next;
l2=l2->next;
}
while(l2||l1){
if(l2){
p->next=l2;
k=l2->val;
l2->val=(k+s)%10;
s=(k+s)/10;
p=l2;
l2=l2->next;
}
if(l1)
{
k=l1->val;
l1->val=(k+s)%10;
s=(k+s)/10;
p=l1;
l1=l1->next;
}
}
if(s!=0)
{
p->next=(struct ListNode*)malloc(sizeof(struct ListNode));
p=p->next;
p->val=1;
p->next=NULL;
}
free(l2);
return l3;
}