2 Add Two Numbers

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
ListNode* head=new ListNode(0);
ListNode* p=head;
int c,s;
c=0;
while(1){
while(l1!=NULL&&l2!=NULL){          //l1和l2都不为空，l1->val+l2->val
s=l1->val+l2->val+c;
c=s/10;
s%=10;
p->next=new ListNode(s);
p=p->next;
l1=l1->next;
l2=l2->next;
}
if(l1==NULL&&l2!=NULL){          //l1为空，l2不为空，0+l2->val
s=l2->val+c;
c=s/10;
s%=10;
p->next=new ListNode(s);
p=p->next;
l2=l2->next;
}
if(l1!=NULL&&l2==NULL){          //l1不为空，l2为空，l1->val+0
s=l1->val+c;
c=s/10;
s%=10;
p->next=new ListNode(s);
p=p->next;
l1=l1->next;
}
if(l1==NULL&&l2==NULL){          //l1和l2都为空，处理进位
if(c>0){
p->next=new ListNode(c);
p=p->next;
}
break;
}
}
head=head->next;
return head;
}
};

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
ListNode dummy(-1);
int carry = 0;
ListNode *prev = &dummy;
for (ListNode *pa = l1, *pb = l2;pa != nullptr || pb != nullptr;
pa = pa == nullptr ? nullptr : pa->next,pb = pb == nullptr ? nullptr: pb->next,prev = prev->next) {
const int ai = pa == nullptr ? 0 : pa->val;
const int bi = pb == nullptr ? 0 : pb->val;
const int value = (ai + bi + carry) % 10;
carry = (ai + bi + carry) / 10;
prev->next = new ListNode(value);
}
if (carry > 0)
prev->next = new ListNode(carry);
return dummy.next;
}
};