day1-<两数相加>

题目描述：

 

 

 

 

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

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

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode * head , *result;
        head = result = new ListNode(0);
        int temp = 0;

        while(l1 || l2 || temp)
        {
            if(l1 != NULL)
            {
                temp += l1->val;

            }
            if(l2 != NULL)
            {
                temp += l2->val;
            }


            ListNode * q = new ListNode(temp % 10);
            result->next = q;
            result = result->next;
//            cout << result->val << " ";
            temp = temp / 10;
            if(l1 != NULL)
            {
                l1 = l1->next;
            }
            if(l2 != NULL)
            {
                l2 = l2->next;
            }
        }
        return head->next;
    }
};

void printValue(ListNode* L)
{
    while (L!=NULL)
    {
        cout << L->val << " ";
        L = L->next;
    }
}

int main()
{
    ListNode* l1, *l2, *head1, *head2, *q;
    Solution S;
    l1 = head1 = new ListNode;
    l2 = head2 = new ListNode;

    int n;
    cin >> n;
    for(int i = 0;i < n;++i)
    {
        int temp = 0;
        cin >> temp;
        q = new ListNode;
        q->val = temp;
        l1->next = q;
        l1 = l1->next;
    }
    l1->next = NULL;

    for(int i = 0;i < n;++i)
    {
        int temp = 0;
        cin >> temp;
        q = new ListNode;
        q->val = temp;
        l2->next = q;
        l2 = l2->next;
    }
    l2->next = NULL;

    ListNode* l3 = S.addTwoNumbers(head1,head2);
    if(l3 == NULL)
    {
        cout << "什么也不是" << endl;
    }
    printValue(l3->next);


    return 0;
}

 心得：

调试了好久，后来发现这几行特别重要：

if(l1 != NULL)
            {
                l1 = l1->next;
            }
            if(l2 != NULL)
            {
                l2 = l2->next;
            }

没有加if判断句的话，程序会发生执行错误！

head = result = new ListNode(0);
这一行也很重要，初始化值为0，要不然也会出错，这个是节点初始化的意思、