算法课程Leetcode作业第三周技术博客

算法课程Leetcode作业第三周技术博客

题目：2. Add Two Numbers 难度：medium

题目描述

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.

Examples:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

分析

用线性链表表示加法中的每一位，将不存在的位定为0，注意进位就可以解决

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* l3 = nullptr;
        ListNode* l3_h = nullptr;
        int add_1 = 0;
        int left, right;
        int result = 0;
        ListNode* a, *b;
        a = l1;
        b = l2;
        while (a != nullptr || b != nullptr || add_1 != 0) {
            if (a == nullptr) {
                left = 0;
            } else {
                left = a -> val;
            }
            if (b == nullptr) {
                right = 0;
            } else {
                right = b -> val;
            }
            result = (right + left + add_1) % 10;
            if ((left + right + add_1) >= 10) {
                add_1 = 1;
            } else {
                add_1 = 0;
            }
            if (l3_h == nullptr) {
                l3_h = new ListNode(result);
                l3 = l3_h;
            } else {
                l3 -> next = new ListNode(result);
                l3 = l3 -> next;
            }
            if (a != NULL)
            a = a -> next;
            if (b != NULL)
            b = b -> next;
        }
        return l3_h;
    }
};

运行结果

这个结果还是令人比较满意的，基本上不需要再优化了。