笔试题15. LeetCode OJ (2)

2. Add Two Number

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

/**
* 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) {
if(l1 == NULL && l1 == NULL)
{
return NULL;
}
if(l1 == NULL)
{
return l2;
}
if(l2 == NULL)
{
return l1;
}

bool ishead = true;
int increase=0;
ListNode *newHead = NULL;
ListNode *cur = NULL;
while(l1 && l2)
{
ListNode * tmp = new ListNode(l1->val+l2->val);
if(increase != 0)
{
tmp->val+=increase;
}

increase = tmp->val / 10;
tmp->val %= 10;

if(cur != NULL)
{
cur->next = tmp;
cur = cur->next;
}

if(ishead)
{
newHead = tmp;
cur = newHead;
ishead = false;
}

l1=l1->next;
l2=l2->next;
}

while(l1)
{
cur->next = new ListNode(l1->val);
cur = cur->next;
if(increase != 0)
{
cur->val+=increase;
increase = cur->val/10;
cur->val%=10;
}
l1=l1->next;
}
while(l2)
{
cur->next = new ListNode(l2->val);
cur = cur->next;
if(increase != 0)
{
cur->val+=increase;
increase = cur->val/10;
cur->val%=10;
}
l2=l2->next;
}

if(increase != 0)
{
cur->next = new ListNode(increase);
}

return newHead;
}
};