[LeetCode] Add Digits

数字累加问题的精简解决方案

最新推荐文章于 2025-09-12 16:49:27 发布

转载最新推荐文章于 2025-09-12 16:49:27 发布 · 59 阅读

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原文链接：http://www.cnblogs.com/jcliBlogger/p/4734238.html

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#开发工具

本文介绍了一种简洁高效的解决数字累加问题的方法，通过观察规律并使用数学技巧，仅用一行代码即可实现从1到任意数的累加，并针对Python中负数取余的特殊情况进行了额外处理。

Well, if you have no idea of other methods, try to compue the result for all the numbers ranging from 1 to 20 and then you will see the regularity. After you find it, this problem just needs 1-line code.

I write the following code.

1 class Solution { 
2 public:
3     int addDigits(int num) {
4         return num - (num - 1) / 9 * 9; 
5     } 
6 };

This link writes anther more elegant one.

class Solution { 
public:
    int addDigits(int num) {
        return (num - 1) % 9 + 1; 
    } 
};

However, both of them cannot be used in Python since Python says that -1 % 9 = 8 and -1 / 9 = -1. Both the codes above will give a wrong answer for input 0. So you have to handle it separately.

1 class Solution:
2     # @param {integer} num 
3     # @return {integer}
4     def addDigits(self, num):
5         return (num - 1) % 9 + 1 if num else 0