Add Two Numbers

Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

Code

//
//  main.cpp
//  兩個數字的加法操做
//
//  Created by mac on 2019/7/14.
//  Copyright © 2019 mac. All rights reserved.
//

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


//Definition for singly-linked list.
struct ListNode {
      int val;
      ListNode *next;
      ListNode(int x) : val(x), next(NULL) {}
  };


//NULL是否是0？ 是0
class Solution {
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
        ListNode preHead(0), *p = &preHead;
        int extra = 0;
        //若是l1=nullptr 且l2=nullptr 且extra=0 那麼這個循環就結束了
        while (l1 || l2 || extra) {
            if (l1) extra += l1->val, l1 = l1->next;
            if (l2) extra += l2->val, l2 = l2->next;
            p->next = new ListNode(extra % 10);
            extra /= 10;
            p = p->next;
        }
        return preHead.next;
    }
};


int main(int argc, const char * argv[]) {
    // insert code here...
    Solution So;
    ListNode *l1=nullptr;
    //這個地方的邏輯判斷不單單限於數字的運算
    //if語句不會被執行
    if (l1||0) {
        cout<<"執行這句話咯，嘿嘿.."<<endl;
    }
    ListNode *l2=nullptr;
    for (int i=1; i<4; i++) {
        ListNode *p=new ListNode(i);
        p->next=l1;
        l1=p;
        ListNode *q=new ListNode(i+1);
        q->next=l2;
        l2=q;
    }
    ListNode*l3 = So.addTwoNumbers(l1, l2);
    while (l3!=NULL) {
        cout<<l3->val<<endl;
        l3=l3->next;
    }
    cout<<"+++++++++++++++++++++++"<<endl;
    cout<<NULL<<endl;//NULL是0
    
    return 0;
}

運行結果

7
5
3
+++++++++++++++++++++++
0
Program ended with exit code: 0

參考文獻

• https://leetcode.com/problems/add-two-numbers/