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

分析：

/**
 * 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)
            return l2;
        if(l2 == NULL)
            return l1;

        vector<int> v1;
        vector<int> v2;
        ListNode *head=NULL , *rear=NULL;
        while(l1 != NULL)
        {
            v1.push_back(l1->val);
            l1 = l1->next;
        }
        while(l2 != NULL)
        {
            v2.push_back(l2->val);
            l2 = l2->next;
        }

		if(v1.size() < v2.size())
		{
			for(int k=v1.size() ; k<v2.size() ; k++)
				v1.push_back(0);
		}else
		{
			for(int k=v2.size() ; k<v1.size() ; k++)
				v2.push_back(0);
		}
        int temp = 0;
        int value = 0;
        for(int j=0 ; j<v1.size() ; j++)
        {
            int sum = v1[j] + v2[j] + temp;
            temp = sum / 10;
			value = sum % 10;
            ListNode *node = new ListNode(value);
            if(head == NULL)
                head = node;
            if(rear == NULL)
                rear = node;
            else
            {
                rear->next = node;
                rear = rear->next;
            }
        }
        if(temp != 0 && rear!=NULL)
        {
            ListNode *node = new ListNode(temp);
            rear->next = node;
        }
        return head;
    }
};

测试Main函数：

int main()
{
    ListNode *l1=NULL , *r1=NULL, *l2 = NULL , *r2=NULL , *result=NULL;
    int arr1[3] = {2,4,3};
    int arr2[3] = {5,6,4};
    for(int i=0 ; i<3 ; i++)
    {
        ListNode *node1 = new ListNode(arr1[i]);
        ListNode *node2 = new ListNode(arr2[i]);
        if(l1 == NULL)
            l1 = node1;
        if(r1 == NULL)
            r1 = node1;
        else{
            r1->next = node1;
            r1 = r1->next;
        }
        if(l2 == NULL)
            l2 = node2;
        if(r2 == NULL)
            r2 = node2;
        else{
            r2->next = node2;
            r2 = r2->next;
        }
    }
    Solution s;
    result = s.addTwoNumbers(l1,l2);
    for( ; result!=NULL ; result=result->next)
        cout<<result->val<<"->";
    cout<<endl;
	system("pause");
    return 0;
}