You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
if(l1==NULL&&l2==NULL) return NULL;
if(l1==NULL&&l2!=NULL) return l2;
if(l1!=NULL&&l2==NULL) return l1;
ListNode*p1,*p2,*head,*p,*s;
p1=l1;
p2=l2;
int flag=0;
head=(ListNode*)malloc(sizeof(ListNode));
p=head;
while(p1&&p2)
{
s=(ListNode*)malloc(sizeof(ListNode));
flag=flag+p1->val+p2->val;
if(flag>9)
{
s->val=flag-10;
flag=1;
}
else
{
s->val=flag;
flag=0;
}
p->next=s;
p=s;
p1=p1->next;
p2=p2->next;
}
if(!p1&&!p2)
{
if(flag==1)
{
s=(ListNode*)malloc(sizeof(ListNode));
s->val=flag;
p->next=s;
p=s;
}
}
else
{
ListNode* temp;
if(!p1&&p2) temp=p2;
else temp=p1;
while(temp)
{
s=(ListNode*)malloc(sizeof(ListNode));
flag=flag+temp->val;
if(flag>9)
{
s->val=flag-10;
flag=1;
}
else
{
s->val=flag;
flag=0;
}
p->next=s;
p=s;
temp=temp->next;
}
if(flag==1)
{
s=(ListNode*)malloc(sizeof(ListNode));
s->val=flag;
p->next=s;
p=s;
}
}
head=head->next;
p->next=NULL;
return head;
}
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
if(l1==NULL&&l2==NULL) return NULL;
if(l1==NULL&&l2!=NULL) return l2;
if(l1!=NULL&&l2==NULL) return l1;
unsigned long n=0;
unsigned long m=0;
ListNode*p1,*p2,*head,*p,*s;
p1=l1;
p2=l2;
int i=0;
while(p1)
{
n+=(p1->val*pow(10.0,i));
i++;
p1=p1->next;
}
i=0;
while(p2)
{
m+=(p2->val*pow(10.0,i));
i++;
p2=p2->next;
}
unsigned long res=n+m;
head=(ListNode*)malloc(sizeof(ListNode));
p=head;
if(res==0)
{
s=(ListNode*)malloc(sizeof(ListNode));
s->val=res;
p->next=s;
p=s;
}
while(res/10)
{
s=(ListNode*)malloc(sizeof(ListNode));
int temp=res%10;
res/=10;
s->val=temp;
p->next=s;
p=s;
}
if(res%10!=0)
{
s=(ListNode*)malloc(sizeof(ListNode));
int temp=res%10;
s->val=temp;
p->next=s;
p=s;
}
head=head->next;
p->next=NULL;
return head;
}原文：http://blog.csdn.net/sinat_24520925/article/details/45557329