445. Add Two Numbers II

遍历二个链表，存储在vector数组内；

然后进行加法运算，注意进位，并建立新链表，采取head插入的方式

/**
 * 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) {
        vector<int> left,right;
        while(l1!=NULL)
        {
            left.push_back(l1->val);
            l1=l1->next;
        }
        while(l2!=NULL)
        {
            right.push_back(l2->val);
            l2=l2->next;
        }
        
        ListNode *head=(ListNode*)malloc(sizeof(ListNode));
        head->next=NULL;        
        
        int len1=left.size()-1,len2=right.size()-1;
        int flag =0;//进位标志
        while(len1>=0&&len2>=0)
        {
            ListNode *temp=(ListNode*)malloc(sizeof(ListNode));
            temp->val=(left[len1]+right[len2]+flag)%10;
            temp->next=head->next;
            head->next=temp;
            flag=(left[len1]+right[len2]+flag)/10;
            len1--;len2--;
        }
        
        while(len1>=0)
        {
            ListNode *temp=(ListNode*)malloc(sizeof(ListNode));
            temp->val=(left[len1]+flag)%10;
            temp->next=head->next;
            head->next=temp;
            flag=(left[len1]+flag)/10;
            len1--;
        }
        while(len2>=0)
        {
            ListNode *temp=(ListNode*)malloc(sizeof(ListNode));
            temp->val=(right[len2]+flag)%10;
            temp->next=head->next;
            head->next=temp;
            flag=(right[len2]+flag)/10;
            len2--;
        }
        if(flag) //最高位是否有进位
        {
            ListNode *temp=(ListNode*)malloc(sizeof(ListNode));
            temp->val=flag;
            temp->next=head->next;
            head->next=temp;
        }
        return head->next;
    }
};