2. 两数相加(链表的使用)

Posted 2020-12-23 baboon

题目描述

leetcode - 2：https://leetcode-cn.com/problems/add-two-numbers/

解题关键

• C++ 链表 数据结构的定义和遍历

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 *ans = new ListNode(0);    // 定义ListNode节点
        ListNode *tip = ans;    // 标记ans链表起始点，作为答案范围
        int flag = 0;      // 统计进位
        while(l1 != NULL && l2 != NULL){    // l1和l2链表都没遍历完
            flag += l1->val + l2->val;
            ans->next = new ListNode(flag % 10);
            ans = ans->next;
            flag = flag/10;
            l1 = l1->next;
            l2 = l2->next;
        }
        while(l1 != NULL){  // l1链表都没遍历完
            flag += l1->val;
            ans->next = new ListNode(flag % 10);
            ans = ans->next;
            flag = flag/10;
            l1 = l1->next;
        }
        while(l2 != NULL){  // l2链表都没遍历完
            flag += l2->val;
            ans->next = new ListNode(flag % 10);
            ans = ans->next;
            flag = flag/10;
            l2 = l2->next;
        }
        while(flag){    // 还有进位未处理
            ans->next = new ListNode(flag % 10);
            ans = ans->next;
            flag = flag/10;
        }
        return tip->next;
    }
};