leetcode-202 Happy Number

最新推荐文章于 2022-09-27 11:08:40 发布

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本文介绍了一种算法，用于确定一个数字是否为‘幸福数’。幸福数定义为通过将数字转换为其各位数字的平方和的过程，最终得到1的数字。文章详细解释了算法的工作原理，并提供了实现代码。

Write an algorithm to determine if a number is “happy”.

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

题意清楚。要注意的是可能陷入无限循环中。因此要注意，记录之前出现的数字，一旦发现重复的，就代表陷入死循环，返回false。
时间8ms。
代码：

class Solution {
public:
    unordered_set<int> hashset;
    bool isHappy(int n) {
        hashset.insert(n);
        int tmp=0;
        while(n > 0)
        {
            int i = n%10;
            n=n/10;
            tmp = tmp + i*i;
        }
        if(1 == tmp)
        return true;
        else
        {
            if(hashset.find(tmp) != hashset.end())
            return false;
            else
            isHappy(tmp);
        }
    }
};