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

解题思路:这题很简单，主要考虑进位问题，每次递增两个列表结点，分情况讨论即可.

#include<iostream>
#include<vector>
using namespace std;

struct ListNode {
   int val;
   ListNode *next;
   ListNode(int x) : val(x), next(NULL) {}
};

ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
	ListNode*New_head = new ListNode(0);
	ListNode*Tmp_head = New_head;
	int Ones = 0;
	int Tens = 0;
	ListNode*Pre_node = NULL;
	while (l1 != NULL && l2 != NULL)
	{
		Ones = (l1->val + l2->val + Tmp_head->val) % 10;
		Tens = (l1->val + l2->val + Tmp_head->val) / 10;
		Tmp_head->val  = Ones;
		Tmp_head->next = new ListNode(Tens);          //根据是否进位确定下一个结点的初始值
		l1 = l1->next;
		l2 = l2->next;
		Pre_node = Tmp_head;
		Tmp_head = Tmp_head->next;
	}
	if (l1==NULL && l2!=NULL)
		Pre_node->next = addTwoNumbers(l2, Tmp_head);
	else if (l2 == NULL&&l1!=NULL)
		Pre_node->next = addTwoNumbers(l1, Tmp_head);
	else{
		if (Tmp_head->val == 0){
			Pre_node->next = NULL;
			delete Tmp_head;
		}	
	}
	return New_head;
}

Add Two Numbers