leetcode problem solve 2——Add Two Numbers

        題意就不再贅述了，這裏主要總結一下解題過程中感觸比較深的地方。

       這道題僅僅是medium水平，但是我卻做了兩個多小時.....我覺得主要原因是我一開始覺得很簡單，然後一上來就寫代碼，沒有做好前期的問題剖析工作，導致後面每次提交都出現不同的案例測試無法通過，然後真的就慌亂了，心想：這種問題我居然都無法控制住？？！！然後心態就崩了....開始焦躁，又試圖使自己再次專注解題。做人真的不能驕傲阿，你以爲你自己已經足夠冷靜，足夠理性，這只是你以爲....真的到了上戰場的時候，還是會因爲大意丟掉性命。

       前期的分析工作一定要做好，特殊情況要抽出來，要和普通情況分離開，特殊的提前討論，提前解決，解決了之後，再進行一般情況的討論。

       代碼：

       

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


struct ListNode
{
	int val;
	ListNode() { val = 0; next = NULL; }
	ListNode *next;
	ListNode(int x) : val(x), next(NULL) {}
};

class Solution
{
public:
	Solution() {}
	ListNode* addTwoNumbers(ListNode* l1, ListNode* l2)
	{
		int time = 0;//計算相加次數
		int tenSignal = 0;
		ListNode* resultList = new ListNode(1);//用於保存結果
		ListNode* curNode = resultList;		   //當前操作的節點
		//只有一位數的先討論
		if (l1->next == nullptr && l2->next == nullptr)
		{
			int result = l1->val + l2->val;
			int x = result - 10;
			if (x >= 0)
			{
				resultList->val = x;
				ListNode* node = new ListNode(1);
				curNode->next = node;
				curNode = node;
			}
			else
			{
				resultList->val = result;
			}
			return resultList;
		}
		while (l1 != nullptr || l2 != nullptr)
		{
			int result = 0;
			if (l1 != nullptr && l2 != nullptr)
			{
				result = l1->val + l2->val + tenSignal;
				int x = result - 10;
				if (x >= 0)
				{
					tenSignal = 1;
					result = x;
					if (time == 0)
					{
						resultList->val = x;
					}
					else
					{
						ListNode* node = new ListNode(1);
						node->val = x;
						curNode->next = node;
						curNode = node;
					}
					if (l1->next == nullptr && l2->next == nullptr)
					{
						ListNode* node1 = new ListNode(1);
						curNode->next = node1;
						curNode = node1;
					}
				}
				else
				{
					tenSignal = 0;
					if (time == 0)
					{
						resultList->val = result;
					}
					else
					{
						ListNode* node = new ListNode(1);
						node->val = result;
						curNode->next = node;
						curNode = node;
					}
				}				
				l1 = l1->next;
				l2 = l2->next;

			}
			else if (l1 == nullptr && l2 != nullptr)
			{
				//l1不空，l2空
				result = l2->val + tenSignal;
				int x = result - 10;
				if (x >= 0)
				{
					tenSignal = 1;
					//產生1個節點						 
					ListNode* node2 = new ListNode(0);
					curNode->next = node2;
					curNode = node2;
					if (l2->next == nullptr)
					{
						ListNode* node3 = new ListNode(1);
						curNode->next = node3;
						curNode = node3;
					}
				}
				else
				{
					tenSignal = 0;
					if (time == 0)
					{
						resultList->val = result;
					}
					else
					{
						//產生一個節點
						ListNode* node1 = new ListNode(1);
						node1->val = result;
						curNode->next = node1;
						curNode = node1;
					}
				}
				l2 = l2->next;
			}
			else
			{
				//l1不空，l2空
				result = l1->val + tenSignal;
				int x = result - 10;
				if ( x >= 0 )
				{
					tenSignal = 1;
					//產生1個節點						 
					ListNode* node2 = new ListNode(0);					 					 
					curNode->next = node2;
					curNode = node2;
					if (l1->next == nullptr)
					{
						ListNode* node3 = new ListNode(1);
						curNode->next = node3;
						curNode = node3;
					}
				}
				else
				{
					tenSignal = 0;
					if (time == 0)
					{
						resultList->val = result;
					}
					else
					{
						//產生一個節點
						ListNode* node1 = new ListNode(1);
						node1->val = result;
						curNode->next = node1;
						curNode = node1;
					}
				}
				l1 = l1->next;
			}
			time++;
		}//end while
		curNode->next = nullptr;
		return resultList;
	}//end func
};

int main()
{
	//構造兩條鏈表
	ListNode* l1 = new ListNode(3);
	ListNode* l1_cur = l1;
	ListNode node2(7);
	//ListNode node3(9);
	l1_cur->next = &node2;
	l1_cur = &node2;
	/*l1_cur->next = &node3;
	l1_cur = &node3;*/
	l1_cur->next = nullptr;

	ListNode* l2 = new ListNode(9);
	ListNode* l2_cur = l2;
	ListNode node5(2);
	//ListNode node6(3);
	l2_cur->next = &node5;
	l2_cur = &node5;
	/*l2_cur->next = &node6;
	l2_cur = &node6;*/
	l2_cur->next = nullptr;
	//test
	Solution s;
	ListNode* result = s.addTwoNumbers(l2, l1);
	int time = 0;
	while (result)
	{
		cout <<"result: " << result->val << endl;
		result = result->next;	 
		//cout << "time = " << ++time<< endl;
	}

}

  效果：這次還比較滿意