LeetCode 2 ： Add Two Numbers ---- 单链表相加

原题链接： https://leetcode.com/problems/add-two-numbers/
一：原题内容

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

二：AC代码

/**
* 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)
{
ListNode* pAns,* p;
int flag=0;           //标记余数
bool firstNode=true;  //是否是第一个数，因为需要一个指针指向第一个节点，进而返回整个链表
int a=0;
int b=0;
while(l1||l2||flag)   //注意这里的flag，如果输入 5 5 的话，余数1还得进行一次循环
{
a=b=0;

if(l1)
{
a=l1->val;
l1=l1->next;
}
if(l2)
{
b=l2->val;
l2=l2->next;
}

int sum=a+b+flag;

if(sum>=10)
{
sum-=10;
flag=1;
}
else
flag=0;

if(firstNode)
{
p=new ListNode(sum);
pAns=p;
firstNode=false;
}

/**********/
else
{
p->next=new ListNode(sum);
p=p->next;
}
/**********/

/*对指针的理解又进一步了，下面是上一段代码的错误示例，提醒下自己
else
{
p=new ListNode(num);
}
p=p->next;
*/
}

return pAns;
}
};

# 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
"""
ret=ListNode(0)
ans=ret
flag=0

while True:
if l1:
flag+=l1.val
l1=l1.next
if l2:
flag+=l2.val
l2=l2.next

ret.val=flag%10
flag/=10

if l1 or l2 or flag:
ret.next=ListNode(0)
ret=ret.next
else:
break;

return ans

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