Leetcode117: Add Two Numbers

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) {
        int flag=0;
        ListNode* p = new ListNode(0);
        ListNode* tmp = p;
        while(l1 || l2)
        {
            int val1 = 0;
            if(l1)
            {
                val1 = l1->val;
                l1 = l1->next;
            }
            
            int val2 = 0;
            if(l2)
            {
               val2 = l2->val;
               l2 = l2->next;
            }
            
            int sum = val1 + val2 + flag;
            tmp->next = new ListNode(sum%10);
            flag = sum/10;
            tmp = tmp->next;
        }
        if(flag == 1)
            tmp->next = new ListNode(1);
        
        return p->next;
    }
};

python代码：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
       	l3 = ListNode(-1)
       	head = l3
       	flag = 0
       	sum = 0
       	while l1!=None and l2!=None:
       		sum = l1.val + l2.val + flag
       		flag = sum/10
       		sum %= 10
       		head.next = ListNode(sum)
       		head = head.next
       		l1 = l1.next
       		l2 = l2.next
       	while l1!=None:
       		sum = l1.val + flag
       		flag = sum / 10
       		sum %= 10
       		head.next = ListNode(sum)
       		head = head.next
       		l1 = l1.next
       	while l2!=None:
       		sum = l2.val + flag
        	flag = sum / 10
        	sum %= 10
        	head.next = new ListNode(sum)
        	head = head.next
        	l2 = l2.next
        if flag:
        	head.next = ListNode(flag)
        return l3.next