LeetCode problem 2. Add Two Numbers

深藏阁楼爱情的钟 2022-06-01 01:24 89阅读 0赞

### 问题描述 ###

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.

> 假定两个数都不是0开头，除了数本身就是0。

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### 例子 ###

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

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### 思路 ###

题目没什么难点，就是链表的顺序遍历问题。注意进位就行了，可能最后有一个进位要再创建一个节点，不要漏掉。

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### 代码 ###

/**
     *  C++ 代码
     * Definition for singly-linked list.
     * struct ListNode {
     *     int val;
     *     ListNode *next;
     *     ListNode(int x) : val(x), next(NULL) {}
     * };
     */
    class Solution {
        
    public:
        ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
            ListNode head(-1);
            int f = 0; //标识进位
            ListNode* pre = &head;
            ListNode* pa = l1, *pb = l2;
            int val = 0, a, b;
            while(pa!=nullptr||pb!=nullptr){
    
               a = pa == nullptr?0:pa->val;
               b = pb == nullptr?0:pb->val;
               val = a + b + f;
               f = val / 10;
               val = val % 10;
    
               pre->next = new ListNode(val);
    
               pa=pa==nullptr?nullptr:pa->next;
               pb=pb==nullptr?nullptr:pb->next;
               pre = pre->next;        
            }
            //最后判断是否有进位
            if(f>0){
              pre->next = new ListNode(f);
            }
            return head.next;
        }
    };