LeetCode: Add Two Numbers

Problem

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
与Add Binary类似，模拟加法运算即可。

最后的进位容易忘记。

/**
* 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) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (l1 == NULL && l2 == NULL)
return NULL;
ListNode* result = new ListNode(0); // 设置一个哨兵节点，结束时删除
ListNode* current = result;
int carry = 0;
int value = 0;
while(l1 != NULL && l2 != NULL)
{
value = l1->val + l2->val + carry;
current->next = new ListNode(value % 10);
current = current->next;
carry = value / 10;
l1 = l1->next;
l2 = l2->next;
}
while(l1 != NULL)
{
value = l1->val + carry;
current->next = new ListNode(value % 10);
current = current->next;
carry = value / 10;
l1 = l1->next;
}
while(l2 != NULL)
{
value = l2->val + carry;
current->next = new ListNode(value % 10);
current = current->next;
carry = value / 10;
l2 = l2->next;
}
if (carry != 0)
current->next = new ListNode(1);

current = result;
result = result->next;
delete current;
return result;
}
};