LeetCode_Add Two Numbers

题目：

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

思路：计算进位，注意最后一位的处理。

#include<iostream>
using namespace std;
struct ListNode {
      int val;
      ListNode *next;
      ListNode(int x) : val(x), next(NULL) {}
};
ListNode *addTwoNumbers(ListNode *l1, ListNode *l2)
{
	  if(l1 == NULL || l2 == NULL)
	  {
	  	return l1==NULL?l2:l1;
	  }
	  ListNode *head = l1;

	  int len1 = 0;
	  int len2 = 0;

	  ListNode *p1 = l1;
	  ListNode *p2 = l2;

	  while(p1!=NULL)
	  {
	  	len1++;
	  	p1=p1->next;
	  }
	  while(p2!=NULL)
	  {
	  	len2++;
	  	p2=p2->next;
	  }
	  //cout<<len1<<";"<<len2<<endl;
	  ListNode *pre_l1 = l1;
	  ListNode *pre_l2 = l2; 

	  int jinwei = 0;

	  while(l1!=NULL && l2!=NULL)
	  {
	  	int sum = l1->val + l2->val + jinwei;
	  	l1->val = sum%10;
	  	//计算进位
	  	if(sum>=10)
	  	{
	  		jinwei = 1;
		}
		else
		{
			jinwei = 0;
		}
		pre_l1 = l1;
		l1 = l1->next;
		pre_l2 = l2;
		l2 = l2->next;
	  }
	  if(l1==NULL&&l2!=NULL)
	  {
	  	pre_l1->next = l2;
	  	while(l1==NULL&&l2!=NULL)
	  	{
	  		int sum = l2->val + jinwei;
	  		l2->val = sum%10;
	  		if(sum>=10)
	  		{
	  			jinwei = 1;
			}
			else
			{
				jinwei = 0;
			}
			pre_l2 = l2;
			l2 = l2->next;
	  	}
	  }
	  if(l2==NULL&&l1!=NULL)
	  {
	  	while(l2==NULL&&l1!=NULL)
	  	{
	  		int sum = l1->val + jinwei;
	  		l1->val = sum%10;
	  		if(sum>=10)
	  		{
	  			jinwei = 1;
			}
			else
			{
				jinwei = 0;
			}
			pre_l1 = l1;
			l1 = l1->next;
	  	}
	  }
	  if(jinwei == 1 && len1>=len2)
	  {
	  	ListNode *end = new ListNode(jinwei);
	  	//找到最后的节点
	  	pre_l1->next = end;
	  }
	  if(jinwei == 1 && len1<len2)
	  {
	  	ListNode *end = new ListNode(jinwei);
	  	//找到最后的节点
	  	pre_l2->next = end;
	  }
	  return head;
}
int main(void)
{
	//cout<<"l"<<endl;
	ListNode *l1 = new ListNode(2);
	ListNode *l2 = new ListNode(4);
	ListNode *l3 = new ListNode(3);
	l1->next = l2;
	l2->next = l3;
	ListNode *l11 = new ListNode(5);
	ListNode *l21 = new ListNode(6);
	ListNode *l31 = new ListNode(2);
	l11->next = l21;
	l21->next = l31;

	ListNode *p = addTwoNumbers(l1,l11);
	while(p!=NULL)
	{
		cout<<p->val<<" ";
		p=p->next;
	}
	delete l1;
	delete l2;
	delete l3;
	delete l11;
	delete l21;
	delete l31;
	system("pause");
	return 0;
}