力扣 题目2- 两数相加

题目

题解

同时向后遍历 用一个参数做进位 长度不够进行补0

代码

#include<iostream>
#include<vector>
using namespace std;
struct ListNode {
    int val;
    ListNode* next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode* next) : val(x), next(next) {}
};

int loop(ListNode* &l1, ListNode* &l2, ListNode*& result,int back) {
    result->val = (l1->val + l2->val+back) % 10;
    back = (l1->val + l2->val + back) / 10;
    //如果l1与l2不同时为空 或者 back>0(进位)
    if ((l1->next != nullptr || l2->next != nullptr) || back > 0) {
        result->next = new ListNode(back);
        result = result->next;
    }

    //如果下一个都不为空
    if (l1->next != nullptr && l2->next != nullptr) {
        loop(l1->next, l2->next, result, back);
    }
    //如果l1下一个为空则l1补0
    else if(l1->next == nullptr&& l2->next != nullptr)
    {
        l1->next = new ListNode(0);
        loop(l1->next, l2->next, result, back);
    }
    //如果l2下一个为空则l2补0
    else if (l1->next != nullptr&& l2->next == nullptr)
    {
        l2->next = new ListNode(0);
        loop(l1->next, l2->next, result, back);
    }
    return 0;
}

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* result1 = new ListNode(0);
        ListNode* result= result1;
        loop(l1, l2, result1,0);
        return result;
    }
};


void listnum(ListNode& list, vector<int>& vectorlist) {
    ListNode* headlist = &list;
    for (int i = 0; i < vectorlist.size(); i++) {
        ListNode* p;
        p = (struct ListNode*)malloc(sizeof(struct ListNode*));
        p->val = vectorlist[i];
        headlist->next = p;
        headlist = headlist->next;
    }
    headlist->next = NULL;
}


int main() {
    Solution sol;
    ListNode list1(9);
    vector<int> vectorlist1 = { 9,9,9,9,9,9 };
    listnum(list1, vectorlist1);

    ListNode list2(9);
    vector<int> vectorlist2 = { 9,9,9 };
    listnum(list2, vectorlist2);
    ListNode* list = sol.addTwoNumbers(&list1, &list2);
    for (int i = 0; list != nullptr; i++) {
        cout << list->val << endl;
        list = list->next;
    }
}